WHEN … DO

Error-handling statement that performs the statements following DO when the specified error occurs. Available in triggers and stored procedures.

WHEN {<error> [, <error> …] | ANY}
DO <<compound_statement>>

<error>=
{EXCEPTION exception_name | SQLCODE number | GDSCODE errcode}

Argument	Description
`EXCEPTION` <exception_name>	The name of an exception already in the database
`SQLCODE` <number>	A `SQLCODE` error code number
`GDSCODE` <errcode>	An InterBase error code. Use Table 5.5 and strip isc_ before mentioning the error code with GDSCODE usage. For example: GDSCODE lock_conflict.
`ANY`	Keyword that handles any of the above types of errors.
<compound_statement>	Statement or block executed when any of the specified errors occur.

Important: If used, WHEN must be the last statement in a BEGIN…END block. It should come after SUSPEND, if present.

Description: Procedures can handle three kinds of errors with a WHEN statement:

Exceptions raised by EXCEPTION statements in the current procedure, in a nested procedure, or in a trigger fired as a result of actions by such a procedure.
SQL errors reported in SQLCODE.
InterBase error codes.

The WHEN ANY statement handles any of the three types.

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