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SQL2GMS

Author
Erwin Kalvelagen

Overview

SQL2GMS is a tool to convert data from an SQL database into GAMS readable format. The source is any data source accessible through Microsoft's Data Access components including ADO, ODBC and OLEDB. The target is a GAMS Include File or a GAMS GDX File.

When running the executable SQL2GMS.EXE without command line parameters the tool will run interactively with a built-in GUI interface. Alternatively SQL2GMS can be run in batch mode which is useful when calling it directly from a GAMS model using the $call command.

If you need to read data from an MS Access database or MS Excel spreadsheet the accompanying tools MDB2GMS or XLS2GMS may be more appropriate. In some cases it may be useful to use SQL2GMS to read from Access and Excel data sources.

Requirements

SQL2GMS runs only on PC's running Windows (95/98/NT/XP) and with MDAC (Microsoft Data Objects) installed. In many cases this will be installed on your computer. Otherwise it can be downloaded from the Microsoft website https://www.microsoft.com/download.

To use this tool effectively you will need to have a working knowledge of SQL in order to formulate proper database queries. In addition you will need some knowledge on how to connect to your database using ODBC or ADO.

Converting spreadsheet data to GAMS data

Database tables can be considered as a generalization of a GAMS parameter. GAMS parameters are single valued indicating written as a table GAMS parameters have multiple index columns but just one value column. If the table is organized as multi-valued table, a UNION can be used to generate the correct GAMS file.

Besides parameters it is also possible to generate set data. The following tables summarizes some of the possibilities:

  • Single valued table
    GAMS SQL
    parameter d(i,j) /
    $include data.inc
    /;
    
    SELECT city1,city2,distance
    FROM distances
       
  • Multi valued table Use two separate parameters and queries or a parameter with an extra index position and a UNION select.
    GAMS SQL
    parameter sales(year,loc,prd) /
    $include sales.inc
    /;
    parameter profit(year,loc,prd) /
    $include profit.inc
    /;  
    
    SELECT year,loc,prod,sales
    FROM data 
    
    SELECT year,loc,prod,profit
    FROM data
       
    or
    GAMS SQL
    set typ /sales,profit/
    parameter data(year,loc,prd,typ) /
    $include data.inc
    /;  
    
    SELECT year,loc,prod,'sales',sales
    FROM data
    UNION
    SELECT year,loc,prod,'profit',profit
    FROM data
    
  • Single dimension set Make sure elements are unique.
    GAMS SQL
    set i /
    $include set.inc
    /;
    
    SELECT distinct(indexcolumn)
    FROM datatable
    
  • Multi dimensional set Add dummy value field to make sure the elements are separated by a dot or use string concatenation (|| or & depending on DBMS).
    GAMS SQL
    set ij(i,j) /
    $include ij.inc
    /; 
    
    SELECT indx1,indx2," "
    FROM datatable
    
    SELECT indx1&'.'&indx2
    FROM datatable
    
    SELECT indx1||'.'||indx2
    FROM datatable
    

There are no special requirements on the data types used in the database. The data are converted to strings, which is almost always possible. Data types like LONG BINARY may not be convertible to a string, in which case an exception will be raised. In general NULL's should not be allowed to get into a GAMS data structure. The handling of NULL's can be specified in an option.

Example: single-valued table

Consider the simple example table

Table: distances

City1 City2 Distance
SEATTLE NEW-YORK 2.5
SAN-DIEGO NEW-YORK 2.5
SEATTLE CHICAGO 1.7
SAN-DIEGO CHICAGO 1.8
SEATTLE TOPEKA 1.8
SAN-DIEGO TOPEKA 1.4

with the accompanying query:

SELECT City1,City2,Distance
FROM Distances

This can be represented in GAMS as:

set i /seattle, san-diego/;
set j /new-york, chicago, topeka/;
parameter dist(i,j) 'distances' /
$include distances.inc
/;

where the include file distances.inc has been generated using the above query. This file can look like:

* -----------------------------------------------------
* SQL2GMS Version 3.0, November 2006
* Erwin Kalvelagen, GAMS Development Corp
* -----------------------------------------------------
* ADO version: 2.8
* Connection string: Driver={Microsoft Access Driver (*.mdb)}; Dbq=d:\sql2gms\sample.mdb
* Provider: MSDASQL
* Query: SELECT city1, city2, distance
*        FROM distances
* -----------------------------------------------------
SEATTLE.NEW-YORK 2.5
SAN-DIEGO.NEW-YORK 2.5
SEATTLE.CHICAGO 1.7
SAN-DIEGO.CHICAGO 1.8
SEATTLE.TOPEKA 1.8
SAN-DIEGO.TOPEKA 1.4
* -----------------------------------------------------

The standard export format is to consider the last column the value column and the previous columns as the indices. The indices are separated by a dot, allowing the generated include file to be used as part of a parameter declaration statement.

Example: multi-valued table

Consider the table with two value columns:

Table: data

year loc prod sales profit
1997 la hardware 80 8
1997 la software 60 16
1997 nyc hardware 110 5
1997 nyc software 100 10
1997 sfo hardware 80 9
1997 sfo software 50 10
1997 was hardware 120 7
1997 was software 70 20
1998 la hardware 70 6
1998 la software 70 10
1998 nyc hardware 120 7
1998 nyc software 120 14
1998 sfo hardware 90 12
1998 sfo software 70 15
1998 was hardware 130 12
1998 was software 80 15

A simple way to import this into GAMS is to use two parameters and two SQL queries. The SQL queries can look like:

SELECT year,loc,prod,sales
FROM data
 
SELECT year,loc,prod,profit
FROM data

If the results are stored in include files sales.inc and profit.inc then this can be read into GAMS as follows:

parameter sales(year,loc,prd) /
$include sales.inc
/;
parameter profit(year,loc,prd) /
$include profit.inc
/;

The operation can also be performed in one big swoop by using a different GAMS datastructure:

set typ /sales,profit/
parameter data(year,loc,prd,typ) /
$include data.inc
/;

This parameter has an extra index typ which indicates the data type. To generate the correct include file we can use the following query:

SELECT year,loc,prod,'sales',sales
FROM data
UNION
SELECT year,loc,prod,'profit',profit
FROM data

The generated include file will look like:

* -----------------------------------------------------
* SQL2GMS Version 3.0, November 2006
* Erwin Kalvelagen, GAMS Development Corp
* -----------------------------------------------------
* ADO version: 2.8
* Connection string: Driver={Microsoft Access Driver (*.mdb)}; Dbq=d:\sql2gms\sample.mdb
* Provider: MSDASQL
* Query: SELECT year,loc,prod,'sales',sales
*        FROM data
*        UNION
*        SELECT year,loc,prod,'profit',profit
*        FROM data
* -----------------------------------------------------
1997.la.hardware.profit 8
1997.la.hardware.sales 80
1997.la.software.profit 16
1997.la.software.sales 60
1997.nyc.hardware.profit 5
1997.nyc.hardware.sales 110
1997.nyc.software.profit 10
1997.nyc.software.sales 100
1997.sfo.hardware.profit 9
1997.sfo.hardware.sales 80
1997.sfo.software.profit 10
1997.sfo.software.sales 50
1997.was.hardware.profit 7
1997.was.hardware.sales 120
1997.was.software.profit 20
1997.was.software.sales 70
1998.la.hardware.profit 6
1998.la.hardware.sales 70
1998.la.software.profit 10
1998.la.software.sales 70
1998.nyc.hardware.profit 7
1998.nyc.hardware.sales 120
1998.nyc.software.profit 14
1998.nyc.software.sales 120
1998.sfo.hardware.profit 12
1998.sfo.hardware.sales 90
1998.sfo.software.profit 15
1998.sfo.software.sales 70
1998.was.hardware.profit 12
1998.was.hardware.sales 130
1998.was.software.profit 15
1998.was.software.sales 80
* -----------------------------------------------------

Index mapping

In some cases the index elements used in the database are not the same as in the GAMS model. E.g. consider the case where the GAMS model has defined a set as:

set i /NY,DC,LA,SF/;

Now assume a data table looks like:

Table: example table

city value
new york 100
los angeles 120
san francisco 105
washington dc 102

This means we have to map ‘new york' to ‘NY' etc. This mapping can be done in two places: either in GAMS or in the database.

Index mapping done in GAMS

When we export the table directly (with the option ‘Quote Blanks' turned on), we get:

* -----------------------------------------------------
* SQL2GMS Version 3.0, November 2006
* Erwin Kalvelagen, GAMS Development Corp
* -----------------------------------------------------
* ADO version: 2.8
* Connection string: Driver={Microsoft Access Driver (*.mdb)}; Dbq=d:\sql2gms\sample.mdb
* Provider: MSDASQL
* Query: SELECT city, value
*        FROM [example table]
* -----------------------------------------------------
'new york' 100
'los angeles' 120
'san francisco' 105
'washington dc' 102
* -----------------------------------------------------

As the index elements contain blanks, the option Quote Blanks was used. To import this file and convert it to a different index space we can use the following GAMS code:

set i /NY,DC,LA,SF/;
 
set idb 'from database' /
'new york',
'washington dc',
'los angeles',
'san francisco'
/;
 
parameter dbdata(idb) /
$include data.inc
/;
 
set mapindx(i,idb) /
  NY.'new york'
  DC.'washington dc'
  LA.'los angeles'
  SF.'san francisco'
/;
 
parameter data(i);
data(i) = sum(mapindx(i,idb), dbdata(idb));
display data;

Index mapping done in Database

The second approach is to handle the mapping inside the database. We can introduce a mapping table that looks like:

Table: mapcity

city gcity
new york la
los angeles ny
san francisco sf
washington dc dc

This table can be used in a join to export the data in a format we can use by executing the query:

SELECT gcity, value
FROM [example table],mapcity
WHERE [example table].city=mapcity.city

The GAMS import step could look like:

set i /NY,DC,LA,SF/;
 
parameter data(i) /
$include data.inc
/;
display data;

where the data file looks like:

* -----------------------------------------------------
* SQL2GMS Version 3.0, November 2006
* Erwin Kalvelagen, GAMS Development Corp
* -----------------------------------------------------
* ADO version: 2.8
* Connection string: Driver={Microsoft Access Driver (*.mdb)}; Dbq=d:\sql2gms\sample.mdb
* Provider: MSDASQL
* Query: SELECT gcity, value
*        FROM [example table], mapcity
*        WHERE [example table].city=mapcity.city
* -----------------------------------------------------
la 120
ny 100
sf 105
dc 102
* -----------------------------------------------------

Note: MS Access allows table names with embedded blanks. In that case the table name can be surrounded by square brackets. Other databases may not allow this.

Connection Strings

The connection string determines to which database the tool will try to connect. You can give simply the name of an ODBC Data Source or provide much more elaborate connection strings. Here is an example list:

  • ODBC Examples
    SourceConnection String
    ODBC Data Source
    MyDSN
    ODBC Data Source
    DSN=MyDSN
    ODBC DSN with userid and password
    DSN=xxx;UID=yyy;PWD=zzz;
    ODBC File DSN
    FILEDSN=d:\ppp\fff.dsn;UID=yyy;PWD=zzz;
    ODBC DSN-less Text Driver
    Driver={Microsoft Text Driver (*.txt; *.csv)};Dbq=d:\ppp\; Extensions=asc,csv,tab,txt;Persist Security Info=False
    (Note: the filename is used in the FROM clause in the query string.)
    ODBC DSN-less MS Access Driver
    Driver={Microsoft Access Driver (*.mdb)};Dbq=d:\ppp\fff.mdb;Uid=yyy;Pwd=zzz;
    ODBC DSN-less driver for MS SQL Server
    Driver={SQL Server};Server=sss;Database=ddd;Uid=yyy;Pwd=zzz;
    ODBC DSN-less MS Access Driver
    Driver={Microsoft Access Driver (*.mdb)};Dbq=d:\ppp\fff.mdb;Uid=yyy;Pwd=zzz;
    ODBC DSN-less driver for MS SQL Server
    Driver={SQL Server};Server=sss;Database=ddd;Uid=yyy;Pwd=zzz;
    ODBC Driver for Oracle
    Driver={Microsoft ODBC for Oracle};Server=sss;Uid=yyy;Pwd=zzz
    ODBC Driver for Oracle (old)
    Driver={Microsoft ODBC Driver for Oracle};ConnectString=sss; Uid=yyy; Pwd=zzz;
    ODBC driver for MySQL
    DRIVER={MySQL ODBC 3.51 Driver};SERVER=localhost;DATABASE=test; UID=xxx;PWD=yyy;OPTION=3
    See http://www.mysql.com/products/myodbc/manual_toc.html
    ODBC driver for Interbase 6/Firebird
    DRIVER={XTG Systems InterBase6 ODBC driver};DB=localhost:d:\gams projects\sql2gms\ver2.0\ib.gdb;UID=xxx;PWD=yy
    See http://www.xtgsystems.com
  • OLE DB Examples
    SourceConnection String
    OLE DB Data link file
    File name=d:\ppp\fff.udl;
    OLE DB Provider for ODBC Access (Jet)
    Provider=MSDASQL; Driver={SQL Server}; Server=sss; Database= ddd; Uid=yyy; Pwd=zzz;
    OLE DB Provider for ODBC SQL Server
    Provider=MSDASQL; Driver={SQL Server}; Server=sss; Database= ddd; Uid=yyy; Pwd=zzz;
    OLE DB Provider for Microsoft Jet (Access)
    Provider=Microsoft.Jet.OLEDB.4.0; Data Source=d:\ppp\fff.mdb; User Id=yyy; Password=zzz;
    OLE DB Provider for Microsoft Jet (Access) with System Database
    Provider=Microsoft.Jet.OLEDB.4.0; Data Source=d:\ppp\fff.mdb; Jet OLEDB:System Database=fff.mdw;
    Specify user id and password in the U=xxx and P=zzz SQL2GMS options. If MDB file has a password, add: Jet OLEDB:Database Password= xxx;.
    OLE DB Provider for SQL Server
    Provider=sqloledb; Network Library=DBMSSOCN; Data Source=ddd ; Initial Catalog=ccc; User Id=yyy; Password=zzz;
    OLE DB Provider for SQL Server with trusted connection security
    Provider=sqloledb; Network Library=DBMSSOCN; Data Source=ddd; Initial Catalog=ccc; Trusted_Connection=yes;
  • MS Remote Examples
    SourceConnection String
    MS Remote - Access (Jet) through ODBC DSN
    Remote Server=http://xxx; Remote Provider=MSDASQL; DSN= nnn; Uid=yyy; Pwd=zzz;
    MS Remote - Access (Jet) through OLE DB Provider
    Provider=MS Remote; Remote Server=http://xxx; Remote Provider=Microsoft.Jet.OLEDB.4.0; Data Source=d:\ppp\fff.mdb; Uid=yyy; Pwd=zzz;
    MS Remote - Access (Jet) through OLE DB Provider with an RDS Datafactory Custom Handler
    Provider=MS Remote; Remote Server=http://xxx; Handler=MSDFMAP.Handler; Data Source=MyConnectTag
    The entry in \winnt\Msdfmap.ini is:
    [connect MyConnectTag]
    Access=ReadWrite
    Connect="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=xxx.mdb; User Id=yyy; Password=zzz;"
    MS Remote - SQL Server using ODBC DSN
    Remote Server=http://xxx; Remote Provider=MSDASQL; Network Library=DBMSSOCN; DSN=nnn; Uid=yyy; Pwd=zzz;
    MS Remote - SQL Server using OLE DB Provider
    Provider=MS Remote; Remote Server=http://xxx; Remote Provider=SQLOLEDB; Network Library=DBMSSOCN; 
    Data Source=nnn; Initial Catalog=ddd; User Id=yyy; Password=zzz;
    MS Remote - SQL Server through OLE DB Provider with an RDS Datafactory Custom Handler
    Provider=MS Remote; Remote Server=http://xxx; Handler=MSDFMAP.Handler; Data Source=MyConnectTag
    The entry in \winnt\Msdfmap.ini is:
    [connect MyConnectTag]
    Access=ReadWrite
    Connect="Provider=SQLOLEDB; Network Library=DBMSSOCN; Data Source=nnn; Initial Catalog=ddd; User Id=yyy; Password=zzz;"

For more information consult the documentation with your database driver. ODBC drivers can be had from several sources: Micrsoft delivers ODBC with a number of drivers; database providers may have likely an ODBC driver for their RDBMS available and finally there are a number of third party ODBC drivers available (e.g. from http://www.easysoft.com ).

ODBC Examples

In this section we show a few examples using SQL2GMS with ODBC data sources.

ODBC Driver Manager

To configure ODBC data sources use the ODBC Data Source Administrator. This tool can be invoked from the Start button menu: Settings|Control Panel, and click on the ODBC Data Sources icon:

_bm0.png

Under Windows XP the sequence is: Control Panel|Performance and Maintenance|Administrative Tools and click on the Data Sources (ODBC) icon. The ODBC Data Source Administrator tool looks like:

_bm1.png

To create a new data source, click the Add button, select a driver, give it a name (this is the DSN name) and configure the data source.

Reading from an MS Access database

There are several ways to export data from an SQL database into a GAMS include file:

  1. Export a CSV (Comma Separated Values) file using Access Export.
  2. Use the MDB2GMS tool.
  3. Use SQL2GMS with a configured ODBC data source. The connection string will look like:
    "DSN=mydsn".
  4. Use SQL2GMS with a DSN-less ODBC connection. In this case we need to specify both the driver and the location of the database file explicitly in the connection string. The connection string will look like:
    "Driver={Microsoft Access Driver (*.mdb)};Dbq=D:\data\mydata.mdb".
  5. Use SQL2GMS with an OLE DB driver. The connection string can look like:
    "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\data\mydata.mdb"

Reading from an MS Excel spreadsheet

There are numerous ways to export data from an Excel spreadsheet into a GAMS include file:

  1. Export a CSV (Comma Separated Values) file using Excel Export.
  2. Use the XLS2GMS tool.
  3. Use the GDXXRW tool.
  4. Use SQL2GMS with an Excel ODBC connection. An example is shown below.

Consider the spreadsheet:

_bm2.png

After configuring a data source ExcelDist that uses the Excel ODBC driver and points to the .XLS file containing the above sheet, we can use the connection string: "DSN=ExcelDist". With the database browser we see:

_bm3.png

I.e. the table name is Sheet1$. We now can formulate the query: SELECT city1,city2,distance FROM [Sheet1$]. We need the brackets to protect the funny table name. The result is:

* -----------------------------------------------------
* SQL2GMS Version 2.0, January 2004
* Erwin Kalvelagen, GAMS Development Corp
* -----------------------------------------------------
* ADO version:       2.7
* Connection string: DSN=ExcelDist
* Query:             SELECT city1,city2,distance
*                    FROM [sheet1$]
* Provider:          MSDASQL
* -----------------------------------------------------
SEATTLE.NEW-YORK 2.5
SAN-DIEGO.NEW-YORK 2.5
SEATTLE.CHICAGO 1.7
SAN-DIEGO.CHICAGO 1.8
SEATTLE.TOPEKA 1.8
SAN-DIEGO.TOPEKA 1.4
* -----------------------------------------------------

Although other tools are often more convenient to use, this approach is useful if you need to select a subsection of the spreadsheet table. It is easy to select just a few columns or rows from a table using a properly formulated SQL query. The skeleton would be: SELECT columns_to_extract FROM [sheet1$] WHERE rows_to_extract.

An example of a more complex spreadsheet is:

_bm4.png

A DSN-less connection string would be: "DRIVER=Microsoft Excel Driver (*.xls); DBQ=d:\gams projects\sql2gms\ver2.0\profit.xls". The browser will show:

_bm5.png

A possible query that maps the two value columns into a GAMS parameter is:

SELECT year,loc,prod,'sales',sales
FROM [profitdata$]
UNION
SELECT year,loc,prod,'profit',profit
FROM  [profitdata$]

The result is:

* -----------------------------------------------------
* SQL2GMS Version 2.0, January 2004
* Erwin Kalvelagen, GAMS Development Corp
* -----------------------------------------------------
* ADO version:       2.7
* Connection string: DRIVER=Microsoft Excel Driver (*.xls);dbq=d:\gams projects\sql2gms\ver2.0\profit.xls;
* Query:             SELECT year,loc,prod,'sales',sales
*                    FROM [profitdata$]
*                    UNION
*                    SELECT year,loc,prod,'profit',profit
*                    FROM  [profitdata$]
* Provider:          MSDASQL
* -----------------------------------------------------
1997.la.hardware.profit 8
1997.la.hardware.sales 80
1997.la.software.profit 16
1997.la.software.sales 60
1997.nyc.hardware.profit 5
1997.nyc.hardware.sales 110
1997.nyc.software.profit 10
1997.nyc.software.sales 100
1997.sfo.hardware.profit 9
1997.sfo.hardware.sales 80
1997.sfo.software.profit 10
1997.sfo.software.sales 50
1997.was.hardware.profit 7
1997.was.hardware.sales 120
1997.was.software.profit 20
1997.was.software.sales 70
1998.la.hardware.profit 6
1998.la.hardware.sales 70
1998.la.software.profit 10
1998.la.software.sales 70
1998.nyc.hardware.profit 7
1998.nyc.hardware.sales 120
1998.nyc.software.profit 14
1998.nyc.software.sales 120
1998.sfo.hardware.profit 12
1998.sfo.hardware.sales 90
1998.sfo.software.profit 15
1998.sfo.software.sales 70
1998.was.hardware.profit 12
1998.was.hardware.sales 130
1998.was.software.profit 15
1998.was.software.sales 80
* -----------------------------------------------------

Reading from a Text File

Microsoft delivers ODBC with a text file driver which allows you to read a text file as if it is database table.

A fixed format file such as:

City1      City2     Distance
SEATTLE    NEW-YORK  2.5
SAN-DIEGO  NEW-YORK  2.5
SEATTLE    CHICAGO   1.7
SAN-DIEGO  CHICAGO   1.8
SEATTLE    TOPEKA    1.8
SAN-DIEGO  TOPEKA    1.4

can be read using Fixed Length setting of the text driver:

_bm6.png

The resulting include file will look like:

* -----------------------------------------------------
* SQL2GMS Version 2.0, January 2004
* Erwin Kalvelagen, GAMS Development Corp
* -----------------------------------------------------
* ADO version:       2.7
* Connection string: DSN=text
* Query:             select city1,city2,distance from odbcdata.txt
* Provider:          MSDASQL
* -----------------------------------------------------
SEATTLE.NEW-YORK 2.5
SAN-DIEGO.NEW-YORK 2.5
SEATTLE.CHICAGO 1.7
SAN-DIEGO.CHICAGO 1.8
SEATTLE.TOPEKA 1.8
SAN-DIEGO.TOPEKA 1.4
* -----------------------------------------------------

A CSV file can be interpreted as a table as well, or any other separated format. We will try to read:

City1;City2;Distance
SEATTLE;NEW-YORK;2.5
SAN-DIEGO;NEW-YORK;2.5
SEATTLE;CHICAGO;1.7
SAN-DIEGO;CHICAGO;1.8
SEATTLE;TOPEKA;1.8
SAN-DIEGO;TOPEKA;1.4

This can be read using:

_bm7.png

The actual formats used are stored by ODBC in an INI file schema.ini (located in the directory of the data files) which can be inspected directly:

[odbcdata.txt]
ColNameHeader=True
Format=FixedLength
MaxScanRows=25
CharacterSet=ANSI
Col1=city1 Char Width 11
Col2=city2 Char Width 11
Col3=distance Float Width 10
 
[odbcdata2.txt]
ColNameHeader=True
Format=Delimited(;)
MaxScanRows=25
CharacterSet=OEM
Col1=City1 Char Width 255
Col2=City2 Char Width 255
Col3=Distance Float

Interactive use

When the tool is called without command line parameters, it will startup interactively. Using it this way, one can specify options such as the connection string, the query and the final destination file (a GAMS include file or a GDX file) using the built-in interactive environment. The main screen contains a number of buttons and edit boxes, which are explained below.

  • Output GAMS Include file (*.INC). If you want to create a GAMS include file, then specify here the destination file. The include file will be an ASCII file that can be read by GAMS using the $include command. If the include file already exists, it will be overwritten.
    _bm8.png
  • Output GDX file (*.GDX). As an alternative to a GAMS include file, the tool can also generate a GDX file. If the GDX file already exists it will be overwritten - it is not possible to append to a GDX file. One or both of the output files need to be specified.
    _bm9.png
  • SQL Query. The SQL Query box is the place to provide the query. Note that the actual area for text can be larger than is displayed: use the cursor-keys to scroll. The query is passed on directly to the RDBMS so the complete power and expressiveness of SQL is available including stored procedures etc. For an exact description of allowed expressions consult a text on your database system.
    _bm10.png
  • Progress Memo. This memo field is used to show progress of the application. Also error messages from the database are printed here. This is a read-only field.
    _bm11.png
  • The edit boxes above all have a drop down list which can be used to access quickly file names and queries that have been used earlier (even from a previous session).
    _bm12.png
  • The tables button will pop up a new window with the contents of the database file selected in the input file edit line. This allows you to see all table names and field names needed to specify a correct SQL query. An exception will be generated if no database file name is specified in the input edit line.
    _bm13.png
  • options button will pop up a window where you can specify a number of options. The connection string is an important option, which needs to be set correctly before a query can be submitted successfully.
    _bm14.png
  • help button will show this help.
    _bm15.png
  • the OK button is pressed the query will be executed and an include file will be generated.
    _bm16.png
  • the batch button will give information on how the current extract command can be executed directly from GAMS in a batch environment. The batch call will be displayed and can be copied onto the clipboard. In the IDE press Ctrl-C or choose Edit|Paste to copy the contents of the clipboard to a GAMS text file.
    _bm17.png
  • close button will exit the application. The current settings will be saved in an INI file so when you run SQL2GMS again all current settings will be restored.
    _bm18.png

Options

The Options window can be created by pressing the options button:

_bm19.png

The following options are available in the options window:

  • User name: Here you can specify the user name for logging in to the RDBMS. For databases without user authentication, this can be left empty.
    _bm20.png
  • Password: this edit box allows you to specify the password for the database system. The characters are echoed as a '*'.
    _bm21.png
  • Connection String: The connection string determines how SQL2GMS talks to the database. For more information see Connection Strings.
    _bm22.png
  • ODBC Data Sources/Drivers: Tthis drop down list can be used to compose a connection string when an ODBC data source or driver is involved. The list will show all configured data sources and all available ODBC drivers.
    _bm23.png
  • Quote blanks: Quote strings if they contain blanks or embedded quotes. If a string does not contain a blank or embedded quotes, it will remain unquoted. If the string contains a single quote the quotes applied will be double quotes and if the string contains already a double quote, the surrounding quotes will be single quotes. (In the special case the string contains both, double quotes are replaced by single quotes). For more information see this example. This option only applies to an output include file.
    _bm24.png
  • Mute: Don't include the extra informational text (such as used query etc.) in the include file.
    _bm25.png
  • No listing: Surround the include file by $offlisting and $onlisting so that the data will not be echoed to the listing file. This can be useful for very large data files, where the listing file would become too large to be handled comfortably.
    _bm26.png
  • Format SQL: If an SQL text is reloaded in the SQL Edit Box, it will be formatted: keywords will be printed in CAPS and the FROM and WHERE clause will be printed on their own line. If this check box is unchecked this formatting will not take place and SQL queries will be shown as is.
    _bm27.png

The following options are only needed in special cases:

  • NULL: This radio box determines how NULL's are handled. A NULL in an index position or a value column will usually make the result of the query useless: the GAMS record will be invalid. To alert you on NULL's the default to throw an exception is a safe choice. In special cases you may want to map NULL's to an empty string or a 'NULL' string.
    clip0001.png
  • Time-out values for connection time and command execution time expressed in seconds. If -1 is specified then it will the use the default value which is 15 seconds for the connection and 30 for the commands. If you set the value to zero, ADO will wait indefinitely.
    clip0002.png

The buttons have an obvious functionality:

  • OK button will accept the changes made.
    _bm29.png
  • Cancel button wil ignore the changes made, and all option settings will revert to their previous values.
    _bm30.png
  • Help button will show this help text.
    _bm31.png
  • Test Connection will try to make a connection to the database using the given connection string.
    _bm32.png
    If the settings are correct you will see something like:
    _bm33.png

The following options can only be specified in an ini file; there is no interactive equivalent:

Key Type Meaning
D Generate debug output
E Allow an empty result set; without this option an empty result set will generate an error
R integer Row batch size; the default is 100 records

Batch use

When calling SQL2GMS directly from GAMS we want to specify all command and options directly from the command line or from a command file. An example is:

C:\tmp> sql2gms C="DSN=sample" O=C:\tmp\data.inc Q="select City1,City2,Distance from Distances"

This call will perform its task without user intervention. The batch facility can be used from inside a GAMS model, e.g.:

parameter c(i,j) 'data from database' /
$call =sql2gms C="DSN=sample" O=C:\tmp\data.inc Q="select City1,City2,Distance from Distances"
$include C:\tmp\data.inc
/;

The $call statement is rather error prone and you will need to spend a little it of time to get the call correct and reliable.

All the possible command line options are listing in command line arguments section. A proper batch call will at least contain the following command line parameters:

  1. C=connectionstring
  2. O=outputincludefile or X=outputgdxfile
  3. Q=querystring

Example

Consider the database table:

Table: data

year loc prod sales profit
1997 la hardware 80 8
1997 la software 60 16
1997 nyc hardware 110 5
1997 nyc software 100 10
1997 sfo hardware 80 9
1997 sfo software 50 10
1997 was hardware 120 7
1997 was software 70 20
1998 la hardware 70 6
1998 la software 70 10
1998 nyc hardware 120 7
1998 nyc software 120 14
1998 sfo hardware 90 12
1998 sfo software 70 15
1998 was hardware 130 12
1998 was software 80 15

We want to extract the following information:

  • The set year
  • The set loc
  • The parameter sales
  • The parameter profit

This can be accomplished using the following GAMS code:

set y 'years' /
$call =sql2gms C="DSN=sample" Q="select distinct(year) from data" O="D:\data\years.inc"
$include d:\data\years.inc
/;
 
set loc 'locations' /
$call =sql2gms C="DSN=sample" Q="select distinct(loc) from data" O="D:\data\locations.inc"
$include d:\data\locations.inc
/;
 
set prd 'products' /hardware, software/;
 
parameter sales(prd,loc,y) /
$call =sql2gms C="DSN=sample" Q="select prod,loc,year,sales from data" O="d:\data\sales.inc"
$include d:\data\sales.inc
/;
display sales;
 
parameter profit(prd,loc,y) /
$call =sql2gms C="DSN=sample" Q="select prod,loc,year,profit from data" O="d:\data\profit.inc"
$include d:\data\profit.inc
/;
display profit;

The $CALL statements assume that sql2gms.exe is in the path. This can be achieved by placing sql2gms.exe in GAMS system directory (the directory where also gams.exe is located; the directory can be easily located in the IDE by looking at GAMS executable path in File|Options|Execute). If sql2gms.exe is not in the search path, you can call it explicitly as:

$call ="D:\util\sql2gms.exe" C="DSN=sample" Q="select prod,loc,year,profit from data" O="d:\data\profit.inc"

The resulting listing file will show:

1  set y 'years' /
INCLUDE    d:\data\years.inc
  4  * -----------------------------------------------------
  5  * SQL2GMS Version 2.0, January 2004
  6  * Erwin Kalvelagen, GAMS Development Corp
  7  * -----------------------------------------------------
  8  * ADO version:       2.7
  9  * Connection string: DSN=sample
 10  * Query:             select distinct(year) from data
 11  * Provider:          MSDASQL
 12  * -----------------------------------------------------
 13   1997
 14   1998
 15  * -----------------------------------------------------
 16  /;
 17
 18  set loc 'locations' /
INCLUDE    d:\data\locations.inc
 21  * -----------------------------------------------------
 22  * SQL2GMS Version 2.0, January 2004
 23  * Erwin Kalvelagen, GAMS Development Corp
 24  * -----------------------------------------------------
 25  * ADO version:       2.7
 26  * Connection string: DSN=sample
 27  * Query:             select distinct(loc) from data
 28  * Provider:          MSDASQL
 29  * -----------------------------------------------------
 30   la
 31   nyc
 32   sfo
 33   was
 34  * -----------------------------------------------------
 35  /;
 36
 37  set prd 'products' /hardware, software/;
 38
 39  parameter sales(prd,loc,y) /
INCLUDE    d:\data\sales.inc
 42  * -----------------------------------------------------
 43  * SQL2GMS Version 2.0, January 2004
 44  * Erwin Kalvelagen, GAMS Development Corp
 45  * -----------------------------------------------------
 46  * ADO version:       2.7
 47  * Connection string: DSN=sample
 48  * Query:             select prod,loc,year,sales from data
 49  * Provider:          MSDASQL
 50  * -----------------------------------------------------
 51  hardware.la.1997 80
 52  software.la.1997 60
 53  hardware.nyc.1997 110
 54  software.nyc.1997 100
 55  hardware.sfo.1997 80
 56  software.sfo.1997 50
 57  hardware.was.1997 120
 58  software.was.1997 70
 59  hardware.la.1998 70
 60  software.la.1998 70
 61  hardware.nyc.1998 120
 62  software.nyc.1998 120
 63  hardware.sfo.1998 90
 64  software.sfo.1998 70
 65  hardware.was.1998 130
 66  software.was.1998 80
 67  * -----------------------------------------------------
 68  /;
 69  display sales;
 70
 71  parameter profit(prd,loc,y) /
INCLUDE    d:\data\profit.inc
 74  * -----------------------------------------------------
 75  * SQL2GMS Version 2.0, January 2004
 76  * Erwin Kalvelagen, GAMS Development Corp
 77  * -----------------------------------------------------
 78  * ADO version:       2.7
 79  * Connection string: DSN=sample
 80  * Query:             select prod,loc,year,profit from data
 81  * Provider:          MSDASQL
 82  * -----------------------------------------------------
 83  hardware.la.1997 8
 84  software.la.1997 16
 85  hardware.nyc.1997 5
 86  software.nyc.1997 10
 87  hardware.sfo.1997 9
 88  software.sfo.1997 10
 89  hardware.was.1997 7
 90  software.was.1997 20
 91  hardware.la.1998 6
 92  software.la.1998 10
 93  hardware.nyc.1998 7
 94  software.nyc.1998 14
 95  hardware.sfo.1998 12
 96  software.sfo.1998 15
 97  hardware.was.1998 12
 98  software.was.1998 15
 99  * -----------------------------------------------------
100  /;
101  display profit;

Indeed the includes contain the correct data sets. The include file summary shows that the $CALL and $INCLUDE statements were executed without errors:

Include File Summary

  SEQ   GLOBAL TYPE      PARENT   LOCAL  FILENAME

    1        1 INPUT          0       0  D:\gams projects\sql2gms\ver2.0\Untitled_1.gms
    2        2 CALL           1       2  =sql2gms C="DSN=sample" Q="select distinct(year) from data" O="D:\data\years.i
                                         nc"
    3        3 INCLUDE        1       3  .d:\data\years.inc
    4       19 CALL           1       7  =sql2gms C="DSN=sample" Q="select distinct(loc) from data" O="D:\data\location
                                         s.inc"
    5       20 INCLUDE        1       8  .d:\data\locations.inc
    6       40 CALL           1      14  =sql2gms C="DSN=sample" Q="select prod,loc,year,sales from data" O="d:\data\sa
                                         les.inc"
    7       41 INCLUDE        1      15  .d:\data\sales.inc
    8       72 CALL           1      20  =sql2gms C="DSN=sample" Q="select prod,loc,year,profit from data" O="d:\data\p
                                         rofit.inc"
    9       73 INCLUDE        1      21  .d:\data\profit.inc

Finally the DISPLAY statements show that the data arrived correctly in the required format:

----     69 PARAMETER sales

                   1997        1998

hardware.la       80.000      70.000
hardware.nyc     110.000     120.000
hardware.sfo      80.000      90.000
hardware.was     120.000     130.000
software.la       60.000      70.000
software.nyc     100.000     120.000
software.sfo      50.000      70.000
software.was      70.000      80.000

----    101 PARAMETER profit

                   1997        1998

hardware.la        8.000       6.000
hardware.nyc       5.000       7.000
hardware.sfo       9.000      12.000
hardware.was       7.000      12.000
software.la       16.000      10.000
software.nyc      10.000      14.000
software.sfo      10.000      15.000
software.was      20.000      15.000

Multi-query batch use

In some cases a number of small queries need to be performed on the same database. To do individual calls to SQL2GMS can become expensive: there is significant overhead in starting Access and opening the database. For these cases we have added the option to do multiple queries in one call. To write several GAMS include files we can use a command file that looks like:

C=DRIVER={Microsoft Access Driver (*.mdb)};dbq=sample.mdb

Q1=select distinct(year) from data
O1=year.inc

Q2=select distinct(loc) from data
O2=loc.inc

Q3=select distinct(prod) from data
O3=prod.inc

Q4=select prod,loc,year,sales from data
O4=sales.inc

Q5=select prod,loc,year,profit from data
O5=profit.inc

We see that the option Qn is matched by an option On. That means that the results of the n-th query are written to the n-th output file.

In case we want to store the results of a multi-query call to a single GDX file, we can use:

C=DRIVER={Microsoft Access Driver (*.mdb)};dbq=sample.mdb
X=sample.gdx

Q1=select distinct(year) from data
S1=year

Q2=select distinct(loc) from data
S2=loc

Q3=select distinct(prod) from data
S3=prd

Q4=select prod,loc,year,sales from data
A4=sales

Q5=select prod,loc,year,profit from data
A5=profit

Here we see that a query Qn is matched by either a set name Sn or a parameter name An (the letter P was taken already: it is used to specify a password). The name of the GDX file is specified with the X option.

For a complete example see section Multi-Query Batch example .

Multi-Query Batch example

As an example database we use the Access table:

Table: data

year loc prod sales profit
1997 la hardware 80 8
1997 la software 60 16
1997 nyc hardware 110 5
1997 nyc software 100 10
1997 sfo hardware 80 9
1997 sfo software 50 10
1997 was hardware 120 7
1997 was software 70 20
1998 la hardware 70 6
1998 la software 70 10
1998 nyc hardware 120 7
1998 nyc software 120 14
1998 sfo hardware 90 12
1998 sfo software 70 15
1998 was hardware 130 12
1998 was software 80 15

We want to extract the following information:

  • The set year
  • The set loc
  • The parameter sales
  • The parameter profit

This can be accomplished using the following GAMS code:

$ontext
 
Example database access with SQL2GMS (ODBC)
 
Multiple queries in one call
 
$offtext
 
$onecho > cmd.txt
C=DRIVER={Microsoft Access Driver (*.mdb)};dbq=%system.fp%sample.mdb
 
Q1=select distinct(year) from data
O1=year.inc
 
Q2=select distinct(loc) from data
O2=loc.inc
 
Q3=select distinct(prod) from data
O3=prod.inc
 
Q4=select prod,loc,year,sales from data
O4=sales.inc
 
Q5=select prod,loc,year,profit from data
O5=profit.inc
$offecho
 
$call =sql2gms @cmd.txt
 
set y years /
$include year.inc
/;
set loc locations /
$include loc.inc
/;
set prd products /
$include prod.inc
/;
 
parameter sales(prd,loc,y) /
$include sales.inc
/;
display sales;
 
parameter profit(prd,loc,y) /
$include profit.inc
/;
display profit;

The same example imported through a GDX file can look like:

$ontext
 
Example database access with SQL2GMS (OLEDB)
 
Multiple queries in one call, store in GDX file
 
$offtext
 
$onecho > cmd.txt
C=Provider=Microsoft.Jet.OLEDB.4.0;Data Source=%system.fp%sample.mdb
X=sample.gdx
 
Q1=select distinct(year) from data
s1=year
 
Q2=select distinct(loc) from data
s2=loc
 
Q3=select distinct(prod) from data
s3=prd
 
Q4=select prod,loc,year,sales from data
a4=sales
 
Q5=select prod,loc,year,profit from data
a5=profit
$offecho
 
$call =sql2gms @cmd.txt
 
$call =gdxviewer sample.gdx
 
set y 'years';
set loc 'locations';
set prd 'products';
parameter sales(prd,loc,y);
parameter profit(prd,loc,y);
 
$gdxin 'sample.gdx'
$load y=year loc prd sales profit
 
 
display sales;
display profit;

The call to gdxviewer will display the gdx file in the stand-alone GDX viewer.

Strategies

Including SQL statements to extract data from a database inside your model can lead to a number of difficulties:

  • The database can change between runs, leading to results that are not reproducible. A possible scenario is a user calling you with a complaint: "the model is giving strange results". You run the model to verify and now the results are ok. The reason may be because the data in the database has changed.
  • There is significant overhead in extracting data from a database. If there is no need to get new data from the database it is better to use a snapshot stored locally in a format directly accessible by GAMS.
  • It is often beneficial to look at the extracted data. A first reason, is just to make sure the data arrived correctly. Another argument is that viewing data in a different way may lead to a better understanding of the data. A complete "under-the-hood" approach may cause difficulties in understanding certain model behavior.

Often it is a good strategy to separate the data extraction step from the rest of the model logic.

If the sub-models form a chain or a tree, like in:

Data extraction --> Data manipulation --> Model definition --> Model solution --> Report writing

we can conveniently use the save/restart facility. The individual submodel are coded as:

  • Step 0: sr0.gms
    $ontext
     
    step 0: data extraction from database
    execute as:  > gams sr0 save=s0
     
    $offtext
     
    set i 'suppliers';
    set j 'demand centers';
     
    parameter demand(j);
    parameter supply(i);
    parameter dist(i,j) 'distances';
     
    $onecho > cmd.txt
    C=Provider=Microsoft.Jet.OLEDB.4.0;Data Source=%system.fp%transportation.mdb
     
    Q1=select name from suppliers
    O1=i.inc
     
    Q2=select name from demandcenters
    O2=j.inc
     
    Q3=select name,demand from demandcenters
    O3=demand.inc
     
    Q4=select name,supply from suppliers
    O4=supply.inc
     
    Q5=select supplier,demandcenter,distance from distances
    O5=dist.inc
    $offecho
     
    $call =sql2gms.exe @cmd.txt
     
    set i /
    $include i.inc
    /;
     
    set j /
    $include j.inc
    /;
     
    parameter demand /
    $include demand.inc
    /;
     
    parameter supply /
    $include supply.inc
    /;
     
    parameter dist /
    $include dist.inc
    /;
     
    display i,j,demand,supply,dist;
    
  • Step 1: sr1.gms
    $ontext
     
    step 1: data manipulation step
    execute as:  > gams sr1 restart=s0 save=s1
     
    $offtext
     
    Scalar f 'freight in dollars per case per thousand miles' /90/ ;
     
    Parameter c(i,j) 'transport cost in thousands of dollars per case';
     
    c(i,j) = f * dist(i,j) / 1000 ;
    
  • Step 2: sr2.gms
    $ontext
     
    step 2: model definition
    execute as:  > gams sr2 restart=s1 save=s2
     
    $offtext
     
    Variables
        x(i,j) 'shipment quantities in cases'
        z       'total transportation costs in thousands of dollars' ;
     
    Positive Variable x ;
     
    Equations
        ecost       'define objective function'
        esupply(i)   'observe supply limit at plant i'
        edemand(j)   'satisfy demand at market j' ;
     
    ecost ..        z  =e= sum((i,j), c(i,j)*x(i,j)) ;
     
    esupply(i) ..   sum(j, x(i,j))  =l=  supply(i) ;
     
    edemand(j) ..   sum(i, x(i,j))  =g=  demand(j) ;
    
  • Step 3: sr3.gms
    $ontext
     
    step 3: model solution
    execute as:  > gams sr3 restart=s2 save=s3
     
    $offtext
     
    option lp=cplex;
     
    Model transport /all/ ;
    Solve transport using lp minimizing z ;
    
  • Step 4: sr4.gms
    $ontext
     
    step 4: report writing
    execute as:  > gams sr4 restart=s3
     
    $offtext
     
    abort$(transport.modelstat <> 1) "model not solved to optimality";
     
    display x.l,z.l;
    

A model that executes all steps can be written as:

execute '=gams.exe sr0 lo=3 save=s0';
abort$errorlevel "step 0 failed";
 
execute '=gams.exe sr1 lo=3 restart=s0 save=s1';
abort$errorlevel "step 1 failed";
 
execute '=gams.exe sr2 lo=3 restart=s1 save=s2';
abort$errorlevel "step 2 failed";
 
execute '=gams.exe sr3 lo=3 restart=s2 save=s3';
abort$errorlevel "step 3 failed";
 
execute '=gams.exe sr4 lo=3 restart=s3';
abort$errorlevel "step 4 failed";

If you only change the reporting step, i.e. generating some output using PUT statements, then you only need to change and re-execute step 4. If you change solver or solver options, then only steps 3 and 4 need to be redone. For a small model like this, this exercise may not be very useful, but when the model is large and every step is complex and expensive, this is a convenient way to achieve quicker turn-around times in many cases.

In some cases the save/restart facility is not appropriate. A more general approach is to save the data from the database in a GDX file, which can then be used by other models. We can use the model from step 0 to store the data in a GDX file:

MDB2GDX1.GMS:

$ontext
 
  Store data from Access database into a GDX file.
 
$offtext
 
execute '=gams.exe sr0 lo=3 gdx=trnsport.gdx';
abort$errorlevel "step 0 failed";
 
execute '=gdxviewer.exe trnsport.gdx';

We can also let SQL2GMS create the GDX file:

MDB2GDX2.GMS:

$ontext
 
  Store data from Access database into a GDX file.
 
$offtext
 
$onecho > cmd.txt
C=Provider=Microsoft.Jet.OLEDB.4.0;Data Source=%system.fp%transportation.mdb
X=%system.fp%transportation.gdx
 
Q1=select name from suppliers
S1=i
 
Q2=select name from demandcenters
S2=j
 
Q3=select name,demand from demandcenters
A3=demand
 
Q4=select name,supply from suppliers
A4=supply
 
Q5=select supplier,demandcenter,distance from distances
A5=dist
$offecho
 
$call =sql2gms.exe @cmd.txt

The first approach has the advantage that a complete audit record is available from the data moved from the database to the GDX file in the sr0.lst listing file. If someone ever wonders what came out of the database and how this was stored in the GDX file, that file gives the answer.

To load the GDX data the following fragment can be used:

GDXTRNSPORT.GMS:

$ontext
 
  Load transportation data from GDX file
 
  Compile time loading
 
$offtext
 
set i 'suppliers';
set j 'demand centers';
 
parameter demand(j);
parameter supply(i);
parameter dist(i,j) 'distances';
 
$gdxin transportation.gdx
$load i j demand supply dist
 
 
display i,j,demand,supply,dist

In one application I had to retrieve data from the database each morning, at the first run of the model. The rest of the day, the data extracted that morning could be used. The following logic can implement this:

$ontext
 
  Retrieve data from data base first run each morning.
 
$offtext
 
$onecho > getdate.txt
C=Provider=Microsoft.Jet.OLEDB.4.0;Data Source=%system.fp%transportation.mdb
Q=select day(now())
O=dbtimestamp.inc
$offecho
 
$if not exist dbtimestamp.inc $call "echo 0 > dbtimestamp.inc"
 
scalar dbtimestamp 'day of month when data was retrieved' /
$include dbtimestamp.inc
/;
 
scalar currentday 'day of this run';
currentday = gday(jnow);
 
display "compare", dbtimestamp,currentday;
 
if (dbtimestamp<>currentday,
 
  execute '=gams.exe sr0 lo=3 gdx=transportation.gdx';
  abort$errorlevel "step 0 (database access) failed";
 
  execute '=sql2gms.exe @getdate.txt'
);

The include file dbtimestamp.inc contains the day of the month (1,..,31) on which the data was extracted from the database. If this file does not exist, we initialize it with 0. We then compare this number with the current day of the month. If the numbers do not agree, we execute the database extraction step and rewrite the dbtimestamp.inc file. This last operation could be done using a PUT statement, but in this case we used an SQL statement.

Command-line Arguments

Argument Description
C=ConnectionString This option is required and specifies which database is to be used and how. Examples of valid connection strings are in Connection Strings. Often the connection string will need to be surrounded by quotes, as in: C="DSN=sample"
O=outputincludefile This option specifies the name of the output file. The format of the output file will be a GAMS include file for a parameter statement. Make sure the directory is writable. UNC names can be used. An output file must be specified for batch operation: i.e. either O= or X= needs to be specified (or both).
On=OutputIncludeFile When multiple queries are used, you can append a number to match a query with an output file:

Q2="select a,b from table"
O2=ab.inc

See section Multi-query batch use
X=OutputGDXfile This option specifies the name of the output file. The format of the output file will be a GAMS GDX file. Make sure the directory is writable. UNC names can be used. An output file must be specified for batch operation: i.e. either O= or X= needs to be specified (or both).
Q=Query This option can be used to specify an SQL query. Queries contain spaces and thus have to be surrounded by double quotes. For the exact syntax of the queries that is accepted by the database we refer to the documentation that comes with your RDBMS.
Qn=Query When multiple queries are used, you can append a number to match a query with an output file:

Q2="select a,b from table"
O2=ab.inc

See section Multi-query batch use
S=setname If we write to a GDX file, use this option to specify the name of a set to be used inside the GDX file.
Sn=setname If multiple queries are used, you can append a number to match the query:

Q2="select i from table"
S2=I

See section Multi-query batch use
Y=setname If we write to a GDX file, use this option to specify the name of a set to be used inside the GDX file. If the set contains SetTexts (strings) these will be exported.
Yn=setname If multiple queries are used, you can append a number to match the query. If the set contains SetTexts (strings) these will be exported:

Q2="select i,iText from table"
S2=I

See section Multi-query batch use
A=parametername If we write to a GDX file, use this option to specify the name of a parameter to be used inside the GDX file.
(Note: MDB2GMS uses P, but P was already taken in SQL2GMS for specifying the password).
An=parametername If multiple queries are used, you can append a number to match the query:

Q2="select i,v from table"
A2=v

See section Multi-query batch use
L Embed the data in $offlisting, $onlisting. A quick way to reduce the size of the listing file.
@filename
@"file name"
Causes the program to read options from a file. If the file name contains blanks, it can be surrounded by double quotes. The option file contains one option per line, in the same syntax as if it were specified on the command line.
N=inifilename Use a different Inifile than the standard sql2gms.ini located in the same directory as the executable sql2gms.exe.
T1=ConnectionTimeOut Indicates how long to wait while establishing a connection before terminating the attempt and generating an error. The value sets, in seconds, how long to wait for the connection to open. Default is 15. If you set the property to zero, ADO will wait indefinitely until the connection is opened. A value of -1 indicates that the default value is to be used. Note: the provider needs to support this functionality.
T2=CommandTimeOut Indicates how long to wait while executing a command before terminating the attempt and generating an error. The value sets, in seconds, how long to wait for a command to execute. Default is 30. If you set the property to zero, ADO will wait indefinitely until the execution is complete. A value of -1 indicates that the default value is to be used. Note: the provider needs to support this functionality.
T=TimeOut Sets both T1 and T2.

$CALL command

The $CALL command in GAMS will execute an external program at compile time. There are two forms:

$call externalprogram
$call =externalprogram

The version without the leading '=' calls the external through the command processor (command.com or cmd.exe). The second version with the '=', bypasses the command processor and directly executes the external program. We mention some of the differences:

  1. Some commands are not external programs but built-in commands of the command processor. Examples are COPY, DIR, DEL, ERASE, CD, MKDIR, MD, REN, TYPE. If you want to execute these commands you will need to use the form $call externalprogram which uses the command processor.
  2. If you want to execute a batch file (.bat or .cmd file) then you will need to use the form $call externalprogram.
  3. If it is important to stop with an appropriate error message if the external program does not exist, only use the form $call =externalprogram. The other form is not reliable in this respect. This can lead to surprising results and the situation is often difficult to debug, so in general we would recommend to use the form: $call =externalprogram.
  4. When calling pure Windows programs it is important to call the second form. The first form will not wait until the external Windows program has finished. If it is important to use a command processor in the invocation of a Windows program, use the START command, as in: $call start /w externalwindowsprogram. Otherwise, it is preferred to use: $call =externalwindowsprogram.
Attention
In general it is recommended to use the $call =externalprogram version for its better error-handling.

When command line arguments need to be passed to the external program, they can be added to the line, separated by blanks:

$call externalprogram parameter1 parameter2
$call =externalprogram parameter1 parameter2

The total length of the command line can not exceed 255 characters. If the program name or the parameters contain blanks or quotes you will need to quote them. You can use single or double quotes. In general the following syntax will work:

$call '"external program" "parameter 1" "parameter 2"'
$call ="external program" "parameter 1" "parameter 2"

It is noted that the first form needs additional quotes around the whole command line due to bugs in the parsing of the $call in GAMS. The second form work without additional quotes only if the = appears outside the double quotes.

Command files

Parameters can be specified in a command file. This is important if the length of the command line exceeds 255 characters, which is a hard limit on the length that GAMS allows for command lines. Instead of specifying a long command line as in:

$call =sql2gms C="DSN=sample" O="c:\My Documents\data.inc" Q="Select * from mytable"

we can use a command line like:

$call =sql2gms @"c:\My Documents\options.txt"

The command file

c:\My Documents\options.txt

can look like:

C=DSN=sample
O=c:\My Documents\data.inc
Q=Select * from mytable

It is possible to write the command file from inside a GAMS model using the $echo command. The following example will illustrate this:

$set cmdfile "c:\windows\temp\commands.txt"
$echo "C=DSN=sample"              >  "%cmdfile%"
$echo "O=E:\models\labor.INC"     >> "%cmdfile%"
$echo "Q=select * from labor"     >> "%cmdfile%"
$call =sql2gms @"%cmdfile%"
parameter p /
$include "E:\models\labor.INC"
/;
display p;

Newer versions of GAMS allow:

$set cmdfile "c:\windows\temp\commands.txt"
$onecho  >  "%cmdfile%"
C=DSN=sample
O=E:\models\labor.INC

Q=select * from labor
$offecho
$call =sql2gms @"%cmdfile%"
parameter p /
$include "E:\models\labor.INC"
/;
display p;

If a query becomes very long, it is possible to spread it out over several lines. To signal a setting will continue on the next line insert the character \ as the last character. E.g.:

Q=select prod,loc,year,'sales',sales from data \
 union \
 select prod,loc,year,'profit',sales from data

Notes

ADO

ActiveX Data Objects. Microsoft's data-access object model. An object-oriented architecture for accessing data stored in SQL databases and related data sources. Accessible from a large number of host languages such as VB, C++, Delphi. Supersedes ODBC. Many SQL databases provide ADO access through either OLEDB or ODBC.

ODBC

An API and driver manager system for accessing data stored in an RDBMS. The API provides applications a way to talk to databases while the driver manager application allows users to install, configure and manage ODBC drivers for different databases.

OLEDB

Driver architecture for SQL databases. A driver is called a OLE DB provider. This is used from ADO.

UNC Names

UNC means Unified Naming Convention. UNC names are a microsoft convention to name files across a network. The general format is:

\\<server>\<share>\<path>\<file>

Examples:

\\athlon\c\My Documents\sql2gms.rtf

GDX Files

A GDX file contains GAMS data in binary format. The following GAMS commands will operate on GDX files: $GDXIN, $LOAD, EXECUTE_LOAD, EXECUTE_UNLOAD. The GDX=filename command line option will save all data to a GDX file. A GDX file can be viewed in the IDE using File|Open.

MDB2GMS

MDB2GMS is a tool to import tables from MS Access databases. This utility directly uses MS Access and DAO (Data Access Objects) resulting in a somewhat simpler interface. It is not needed to specify a connection string, but just a .MDB file. The query mechanism is similar: a query is sent as is to the database server and the result set is translated into a GAMS representation. For more information see MDB2GMS.

XLS2GMS

XLS2GMS is a tool to import information from an Excel spreadsheet. It considers the content of a selected range as GAMS source code. For more information XLS2GMS.

Quotes

Examples of handling of indices when the option "quote blanks" is used:

Input Output Remarks
Hello hello blanks or embedded quotes
"hello" "hello" touched, is quoted already
'hello' 'hello' id.
"hello' "hello' id., but will generate an error in GAMS
o'brien "o'brien"
'o'brien' 'o'brien' touched, will generate an error in GAMS
art"ificial 'art"ificial'
art"ifi'cial "art'ifi'cial"

Compile time commands

All $ commands in GAMS are performed at compile time. All other statements are executed at execution time. This means that a compile time command will be executed before an execution time command, even if it is below. As an example consider:

file batchfile /x.bat/;
put patchfile;
putclose "dir"/;
$call x.bat

This fragment does not work correctly as already during compilation, the $call is executed, while the put statements are only executed after the compilation phase has ended and GAMS has started the execution phase. The above code can be fixed by moving the writing of the batch file to compilation time as in

$echo "dir" > x.bat
$call x.bat

or by moving the external program invocation to execution time:

file batchfile /x.bat/;
put patchfile;
putclose "dir"/;
execute x.bat;

Notice that all $ commands do not include a semi-colon but are terminated by the end-of-line.