$IFEXISTS

Tests the existence of the specified database object or data and executes the following block of the script if object or data exist in the database. 

Syntax 

   1 .  {$IFEXISTS DOMAIN|TABLE|VIEW|TRIGGER|PROCEDURE|
                 EXCEPTION|GENERATOR|UDF|ROLE object_name}
   2 .  {$IFEXISTS select_statement}
  
Example 

The following script drops exception InvalidUserID if the one exists in the database: 

  {$IFEXISTS EXCEPTION  "InvalidUserID" }

     DROP EXCEPTION  "InvalidUserID" ;

  {$ENDIF}
  

The next script alters a procedure: 

  {$IFEXISTS SELECT RDB$PROCEDURE_NAME
             FROM RDB$PROCEDURES
             WHERE RDB$PROCEDURE_NAME = 'GETDBVER'}

     ALTER PROCEDURE GETDBVER
     RETURNS (
         VER INTEGER)
     AS
     begin
       ver =  2 ;
       suspend;
     end;

  {$ENDIF}

SELECT  1  AS FOUND FROM RDB$PROCEDURES
  WHERE RDB$PROCEDURE_NAME = 'PROC';