Stored Procedure Language (PSQL)

ROW_COUNT has been enhanced so that it can now return the number of rows returned by a SELECT statement.

For example, it can be used to check whether a singleton SELECT INTO statement has performed an assignment:

  ..
  BEGIN
    SELECT COL FROM TAB INTO :VAR;

    IF (ROW_COUNT = 0) THEN
      EXCEPTION NO_DATA_FOUND;
  END
  ..
      

See also its usage in the examples below for explicit PSQL cursors.

It is now possible to declare and use multiple cursors in PSQL. Explicit cursors are available in a DSQL EXECUTE BLOCK structure as well as in stored procedures and triggers.

Syntax pattern

    DECLARE [VARIABLE] <cursor_name> CURSOR FOR ( <select_statement> );
    OPEN <cursor_name>;
    FETCH <cursor_name> INTO <var_name> [, <var_name> ...];
    CLOSE <cursor_name>;
      

Examples

1.

    DECLARE RNAME CHAR(31);
    DECLARE C CURSOR FOR ( SELECT RDB$RELATION_NAME
                              FROM RDB$RELATIONS );
    BEGIN
      OPEN C;
      WHILE (1 = 1) DO
      BEGIN
        FETCH C INTO :RNAME;
        IF (ROW_COUNT = 0) THEN
          LEAVE;
        SUSPEND;
      END
      CLOSE C;
    END
      

2.

    DECLARE RNAME CHAR(31);
    DECLARE FNAME CHAR(31);
    DECLARE C CURSOR FOR ( SELECT RDB$FIELD_NAME
                           FROM RDB$RELATION_FIELDS
                           WHERE RDB$RELATION_NAME = :RNAME
                           ORDER BY RDB$FIELD_POSITION );
    BEGIN
      FOR
        SELECT RDB$RELATION_NAME
        FROM RDB$RELATIONS
        INTO :RNAME
      DO
      BEGIN
        OPEN C;
        FETCH C INTO :FNAME;
        CLOSE C;
        SUSPEND;
      END
    END
      

Defaults can now be declared for stored procedure arguments.

The syntax is the same as a default value definition for a column or domain, except that you can use '=' in place of 'DEFAULT' keyword.

Arguments with default values must be last in the argument list; that is, you cannot declare an argument that has no default value after any arguments that have been declared with default values. The caller must supply the values for all of the arguments preceding any that are to use their defaults.

For example, it is illegal to do something like this:   supply arg1, arg2, miss arg3, set arg4...

Substitution of default values occurs at run-time. If you define a procedure with defaults (say P1), call it from another procedure (say P2) and skip some final, defaulted arguments, then the default values for P1 will be substituted by the engine at time execution P1 starts. This means that, if you change the default values for P1, it is not necessary to recompile P2.

However, it is still necessary to disconnect all client connections, as discussed in the Borland InterBase 6 beta "Data Definition Guide" (DataDef.pdf), in the section "Altering and dropping procedures in use".

Examples

   CONNECT ... ;
   SET TERM ^;
   CREATE PROCEDURE P1 (X INTEGER = 123)
   RETURNS (Y INTEGER)
   AS
   BEGIN
     Y = X;
     SUSPEND;
   END ^
   COMMIT ^
   SET TERM ;^

   SELECT * FROM P1;

              Y
   ============

            123

   EXECUTE PROCEDURE P1;

              Y
   ============
            123

   SET TERM ^;
   CREATE PROCEDURE P2
   RETURNS (Y INTEGER)
   AS
   BEGIN
     FOR SELECT Y FROM P1 INTO :Y
     DO SUSPEND;
   END ^
   COMMIT ^
   SET TERM ;^

   SELECT * FROM P2;

              Y
   ============

            123

   SET TERM ^;
   ALTER PROCEDURE P1 (X INTEGER = CURRENT_TRANSACTION)
            RETURNS (Y INTEGER)
   AS
   BEGIN
     Y = X;
    SUSPEND;
   END; ^
   COMMIT ^
   SET TERM ;^

   SELECT * FROM P1;

              Y
   ============

           5875

   SELECT * FROM P2;

              Y
   ============

            123

   COMMIT;

   CONNECT  ... ;

   SELECT * FROM P2;

              Y
   ============

           5880

      

New LEAVE <label> syntax now allows PSQL loops to be marked with labels and terminated in Java style. The purpose is to stop execution of the current block and unwind back to the specified label. After that execution resumes at the statement following the terminated loop.

Syntax pattern

    <label_name>: <loop_statement>
    ...
    LEAVE [<label_name>]
      

where <loop_statement> is one of: WHILE, FOR SELECT, FOR EXECUTE STATEMENT.

Examples

1.

   FOR
     SELECT COALESCE(RDB$SYSTEM_FLAG, 0), RDB$RELATION_NAME
       FROM RDB$RELATIONS
       ORDER BY 1
     INTO :RTYPE, :RNAME
     DO
     BEGIN
       IF (RTYPE = 0) THEN
         SUSPEND;
       ELSE
         LEAVE; -- exits current loop
     END
      

2.

   CNT = 100;
   L1:
   WHILE (CNT >= 0) DO
   BEGIN
     IF (CNT < 50) THEN
       LEAVE L1; -- exists WHILE loop
     CNT = CNT - l;
   END
      

3.

   STMT1 = 'SELECT RDB$RELATION_NAME FROM RDB$RELATIONS';
   L1:
   FOR
     EXECUTE STATEMENT :STMT1 INTO :RNAME
   DO
   BEGIN
     STMT2 = 'SELECT RDB$FIELD_NAME FROM RDB$RELATION_FIELDS
       WHERE RDB$RELATION_NAME = ';
     L2:
     FOR
       EXECUTE STATEMENT :STMT2 || :RNAME INTO :FNAME
     DO
     BEGIN
       IF (RNAME = 'RDB$DATABASE') THEN
         LEAVE L1; -- exits the outer loop
       ELSE IF (RNAME = 'RDB$RELATIONS') THEN
         LEAVE L2; -- exits the inner loop
       ELSE
         SUSPEND;
     END
   END
      

The set of OLD context variables available in trigger modules is now read-only. An attempt to assign a value to OLD.something will be rejected.

The API client can now extract a simple stack trace Error Status Vector when an exception occurs during PSQL execution (stored procedures or triggers). A stack trace is represented by one string (2048 bytes max.) and consists of all the stored procedure and trigger names, starting from the point where the exception occurred, out to the outermost caller. If the actual trace is longer than 2Kb, it is truncated.

Additional items are appended to the status vector as follows:

   isc_stack_trace, isc_arg_string, <string length>, <string>
      

isc_stack_trace is a new error code with value of 335544842L.

Examples

Metadata creation

  CREATE TABLE ERR (
    ID INT NOT NULL PRIMARY KEY,
    NAME VARCHAR(16));

  CREATE EXCEPTION EX '!';
  SET TERM ^;

  CREATE OR ALTER PROCEDURE ERR_1 AS
  BEGIN
    EXCEPTION EX 'ID = 3';
  END ^

  CREATE OR ALTER TRIGGER ERR_BI FOR ERR
    BEFORE INSERT AS
  BEGIN
    IF (NEW.ID = 2)
    THEN EXCEPTION EX 'ID = 2';

    IF (NEW.ID = 3)
    THEN EXECUTE PROCEDURE ERR_1;

    IF (NEW.ID = 4)
    THEN NEW.ID = 1 / 0;
  END ^

  CREATE OR ALTER PROCEDURE ERR_2 AS
  BEGIN
    INSERT INTO ERR VALUES (3, '333');
  END ^
      

1. User exception from a trigger:

  SQL" INSERT INTO ERR VALUES (2, '2');
  Statement failed, SQLCODE = -836
  exception 3
  -ID = 2
  -At trigger 'ERR_BI'
      

2. User exception from a procedure called by a trigger:

  SQL" INSERT INTO ERR VALUES (3, '3');
  Statement failed, SQLCODE = -836
  exception 3
  -ID = 3
  -At procedure 'ERR_1'
  At trigger 'ERR_BI'
      

3. Run-time exception occurring in trigger (division by zero):

  SQL" INSERT INTO ERR VALUES (4, '4');
  Statement failed, SQLCODE = -802
  arithmetic exception, numeric overflow, or string truncation
  -At trigger 'ERR_BI'
      

4. User exception from procedure:

  SQL" EXECUTE PROCEDURE ERR_1;
  Statement failed, SQLCODE = -836
  exception 3
  -ID = 3
  -At procedure 'ERR_1'
      

5. User exception from a procedure with a deeper call stack:

  SQL" EXECUTE PROCEDURE ERR_2;
  Statement failed, SQLCODE = -836
  exception 3
  -ID = 3
  -At procedure 'ERR_1'
  At trigger 'ERR_BI'
  At procedure 'ERR_2'
      

In PSQL, supported UDFs, e.g. RDB$SET_CONTEXT, can be called as though they were void functions (a.k.a “procedures” in Object Pascal). For example:

  BEGIN
     ...
     RDB$SET_CONTEXT('USER_TRANSACTION', 'MY_VAR', '123');
     ...
  END