Embedded SQL means that you can use SQL statements through a host programming language, C/C++, COBOL, and FORTRAN. FORTRAN is used as an example in this article.
You include SQL statements as part of the source code for an application. The source code is compiled and linked with the appropriate language-specific facilities. The SQL statements are executed in the context of the application.
Mimer SQL supports embedded SQL for FORTRAN according to the ISO standard.
The ESQL preprocessor processes SQL statements embedded in the host language. SQL statements are identified by the leading delimiter “EXEC SQL”, e.g. “EXEC SQL DELETE FROM HOTEL”.
You must declare host variables used in SQL statements within the SQL DECLARE SECTION, delimited by the statements BEGIN DECLARE SECTION and END DECLARE SECTION.
The following is an example that connects to the database defined as the default. All rows are then fetched from the table INFORMATION_SCHEMA.TABLES.
This example is stored in a file called simple.efo (used in the call to esql below):
PROGRAM SQLEX EXEC SQL BEGIN DECLARE SECTION CHARACTER*5 SQLSTATE CHARACTER*128 SCHEMA CHARACTER*128 TABLE CHARACTER*20 TYPE EXEC SQL END DECLARE SECTION EXEC SQL DECLARE MYCURSOR CURSOR FOR + SELECT TABLE_SCHEMA, TABLE_NAME, TABLE_TYPE + FROM INFORMATION_SCHEMA.TABLES C Connect to default database EXEC SQL CONNECT TO '' USER 'SYSADM' USING 'SYSADM' EXEC SQL OPEN MYCURSOR EXEC SQL FETCH MYCURSOR INTO :SCHEMA, :TABLE, :TYPE DO WHILE (SQLSTATE .NE. ‘02000’) WRITE(6,100) SCHEMA, TABLE, TYPE 100 FORMAT(X,A,X,A,X,A) EXEC SQL FETCH MYCURSOR INTO :SCHEMA, :TABLE, :TYPE END DO EXEC SQL CLOSE MYCURSOR EXEC SQL COMMIT EXEC SQL DISCONNECT DEFAULT END
The program is preprocessed as follows:
esql –for simple.efo
The resulting file, ‘simple.for’, is compiled using a FORTRAN-compiler and then linked. When executing the resulting ‘simple’ program, a list of the items selected will be displayed.
You can find a more complete example in example.efo.
Embedded SQL is a straightforward way of writing applications that access databases.