Application Development Guide
You can write applications with SQL statements embedded within a host
language. The SQL statements provide the database interface, while the
host language provides the remaining support needed for the application to
execute.
Table 2 shows an SQL statement embedded in a host language
application. In the example, the application checks the
SQLCODE field of the SQLCA structure to determine
whether the update was successful.
Table 2. Embedding SQL Statements in a Host Language
| Language
| Sample Source Code
|
| C/C++
|
EXEC SQL UPDATE staff SET job = 'Clerk' WHERE job = 'Mgr';
if ( SQLCODE < 0 )
printf( "Update Error: SQLCODE = %ld \n", SQLCODE );
|
| Java (SQLJ)
|
try {
#sql { UPDATE staff SET job = 'Clerk' WHERE job = 'Mgr' };
}
catch (SQLException e) {
println( "Update Error: SQLCODE = " + e.getErrorCode() );
}
|
| COBOL
|
EXEC SQL UPDATE staff SET job = 'Clerk' WHERE job = 'Mgr' END_EXEC.
IF SQLCODE LESS THAN 0
DISPLAY 'UPDATE ERROR: SQLCODE = ', SQLCODE.
|
| FORTRAN
|
EXEC SQL UPDATE staff SET job = 'Clerk' WHERE job = 'Mgr'
if ( sqlcode .lt. 0 ) THEN
write(*,*) 'Update error: sqlcode = ', sqlcode
|
SQL statements placed in an application are not specific to the host
language. The database manager provides a way to convert the SQL syntax
for processing by the host language.
For the C, C++, COBOL or FORTRAN languages, this conversion is
handled by the DB2 precompiler. The DB2 precompiler is invoked using
the PREP command. The precompiler converts embedded SQL
statements directly into DB2 run-time services API calls.
For the Java language, the SQLJ translator converts SQLJ clauses into JDBC
statements. The SQLJ translator is invoked with the SQLJ
command.
When the precompiler processes a source file, it specifically looks for SQL
statements and avoids the non-SQL host language. It can find SQL
statements because they are surrounded by special delimiters. For the
syntax information necessary to embed SQL statements in the language you are
using, see the following:
Table 3 shows how to use delimiters and comments to create valid
embedded SQL statements in the supported compiled host languages.
Table 3. Embedding SQL Statements in a Host Language
| Language
| Sample Source Code
|
| C/C++
|
/* Only C or C++ comments allowed here */
EXEC SQL
-- SQL comments or
/* C comments or */
// C++ comments allowed here
DECLARE C1 CURSOR FOR sname;
/* Only C or C++ comments allowed here */
|
| SQLJ
|
/* Only Java comments allowed here */
#sql c1 = {
-- SQL comments or
/* Java comments or */
// Java comments allowed here
SELECT name FROM employee
};
/* Only Java comments allowed here */
|
| COBOL
|
* See COBOL documentation for comment rules
* Only COBOL comments are allowed here
EXEC SQL
-- SQL comments or
* full-line COBOL comments are allowed here
DECLARE C1 CURSOR FOR sname END-EXEC.
* Only COBOL comments are allowed here
|
| FORTRAN
|
C Only FORTRAN comments are allowed here
EXEC SQL
+ -- SQL comments, and
C full-line FORTRAN comment are allowed here
+ DECLARE C1 CURSOR FOR sname
I=7 ! End of line FORTRAN comments allowed here
C Only FORTRAN comments are allowed here
|
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