Differences in how the Db2 precompiler and coprocessor behave

Precompiler: The Db2 precompiler does not require that a period end each EXEC SQL INCLUDE statement. If a period is specified, the precompiler processes it as part of the statement. If a period is not specified, the precompiler accepts the statement as if a period had been specified.

Coprocessor: The Db2 coprocessor treats each EXEC SQL INCLUDE statement like a COPY statement, and requires that a period end the statement. For example:

IF A = B THEN
    EXEC SQL INCLUDE some_code_here END-EXEC.
ELSE
    . . .
END-IF

Note that the period does not terminate the IF statement.

Precompiler: With the Db2 precompiler, COBOL REPLACE statements and the REPLACING phrase of the COPY statement act on the expanded source created from the EXEC SQL statement. COBOL rules for REPLACE and REPLACING are used.

Coprocessor: With the Db2 coprocessor, REPLACE and COPY . . . REPLACING statements act on the original source program, including EXEC SQL statements.

Different behavior can result, as in the following example:

REPLACE == ABC == By == XYZ ==. 
01  G. 
    02  ABC PIC X(10). 
    . . .
    EXEC SQL SELECT * INTO :G.ABC FROM TABLE1 END-EXEC 

With the precompiler, the reference to G.ABC will appear as ABC of G in the expanded source and will be replaced with XYZ of G. With the coprocessor, replacement will not occur, because ABC is not delimited by separators in the original source string G.ABC.

Precompiler: The Db2 precompiler ignores any code that follows END-EXEC statements on the same line.

Coprocessor: The Db2 coprocessor processes code that follows END-EXEC statements on the same line.

Precompiler: The Db2 precompiler does not require that host variable references be unique. The first definition that maps to a valid Db2 data type is used.

Coprocessor: The Db2 coprocessor requires that each host variable reference be unique. The coprocessor diagnoses nonunique references to host variables. You must fully qualify host variable references to make them unique or use the QUALIFY compiler option.

Precompiler: The Db2 precompiler requires that EXEC SQL statements start in columns 12 through 72. Continuation lines of the statements can start anywhere in columns 8 through 72.

Coprocessor: The Db2 coprocessor requires that all lines of an EXEC SQL statement, including continuation lines, be coded in columns 12 through 72.

Precompiler: With the Db2 precompiler, a COBOL alphanumeric data item can be used as a host variable to hold Db2 character data that has subtype FOR BIT DATA. An explicit EXEC SQL DECLARE VARIABLE statement that declares that host variable as FOR BIT DATA is not required.

Coprocessor: With the Db2 coprocessor, a COBOL alphanumeric data item can be used as a host variable to hold Db2 character data that has subtype FOR BIT DATA if an explicit EXEC SQL DECLARE VARIABLE statement for that host variable is specified in the COBOL program. For example:

EXEC SQL DECLARE :HV1 VARIABLE FOR BIT DATA END-EXEC.

As an alternative to adding EXEC SQL DECLARE . . . FOR BIT DATA statements, you can use the NOSQLCCSID compiler option. For details, see the related reference about code-page determination below.

Precompiler: With the Db2 precompiler, if you pass host variables that might be located at different addresses when the program is called more than once, the called program must reset SQL-INIT-FLAG. Resetting this flag indicates to Db2 that storage must be initialized when the next SQL statement runs. To reset the flag, insert the statement MOVE ZERO TO SQL-INIT-FLAG in the PROCEDURE DIVISION of the called program ahead of any executable SQL statements that use those host variables.

Coprocessor: With the Db2 coprocessor, the called program does not need to reset SQL-INIT-FLAG. An SQL-INIT-FLAG is automatically defined in the program to aid program portability. However, statements that modify SQL-INIT-FLAG, such as MOVE ZERO TO SQL-INIT-FLAG, have no effect on the SQL processing in the program.

Precompiler: With the Db2 precompiler, an SQL host variable containing FILLER data items is not flagged with an error message.

IGYPS0294-S SQL host variable reference "data-item" was defined with a contained "FILLER" 
data item, which is not valid for an SQL host variable. The statement was discarded.

For reference, see Host structures in COBOL in Programming for Db2 for z/OS.