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3.12.3 ifdef, ifndef, else, elif and endif directives

You can use the following directives to compile code sections conditionally:

EXEC SQL ifdef name;

Checks a name and processes subsequent lines if name has been created with EXEC SQL define name.

EXEC SQL ifndef name;

Checks a name and processes subsequent lines if name has not been created with EXEC SQL define name.

EXEC SQL else;

Starts processing an alternative section to a section introduced by either EXEC SQL ifdef name or EXEC SQL ifndef name.

EXEC SQL elif name;

Checks name and starts an alternative section if name has been created with EXEC SQL define name.

EXEC SQL endif;

Ends an alternative section.

Example:

exec sql ifndef TZVAR;
exec sql SET TIMEZONE TO 'GMT';
exec sql elif TZNAME;
exec sql SET TIMEZONE TO TZNAME;
exec sql else;
exec sql SET TIMEZONE TO TZVAR;
exec sql endif;