GOTO Statements

A GOTO statement unconditionally transfers the control from the current statement to a labeled statement. The GOTO statement changes the execution logic. Therefore, use this statement only when necessary. Alternatively, you can use the EXCEPTION statement to handle issues in special scenarios. To run a GOTO statement, the labeled statement must be unique.

Syntax

label declaration ::=

goto statement ::=

Examples

postgres=# CREATE OR REPLACE PROCEDURE GOTO_test()
AS 
DECLARE
    v1  int;
BEGIN
    v1  := 0;
        LOOP
        EXIT WHEN v1 > 100;
                v1 := v1 + 2;
                if v1 > 25 THEN
                        GOTO pos1;
                END IF;
        END LOOP;
<<pos1>>
v1 := v1 + 10;
raise info 'v1 is %. ', v1;
END;
/

call GOTO_test();

Constraints

Using GOTO statements has the following constraints:

  • A GOTO statement does not allow multiple labeled statements even if the statements are in different blocks.

    BEGIN
      GOTO pos1; 
      <<pos1>>
      SELECT * FROM ...
      <<pos1>>
      UPDATE t1 SET ...
    END;
    
  • A GOTO statement cannot transfer control to the IF, CASE, or LOOP statement.

    BEGIN
       GOTO pos1; 
       IF valid THEN
         <<pos1>>
         SELECT * FROM ...
       END IF;
     END;
    
  • A GOTO statement cannot transfer control from one IF clause to another, or from one WHEN clause in the CASE statement to another.

    BEGIN 
       IF valid THEN
         GOTO pos1;
         SELECT * FROM ...
       ELSE
         <<pos1>>
         UPDATE t1 SET ...
       END IF;
     END;
    
  • A GOTO statement cannot transfer control from an outer block to an inner BEGIN-END block.

    BEGIN
       GOTO pos1;  
       BEGIN
         <<pos1>>
         UPDATE t1 SET ...
       END;
     END;
    
  • A GOTO statement cannot transfer control from an exception handler to the current BEGIN-END block. However, a GOTO statement can transfer control to the upper-layer BEGIN-END block.

    BEGIN
       <<pos1>>
       UPDATE t1 SET ...
       EXCEPTION
         WHEN condition THEN
            GOTO pos1;
     END;
    
  • To branch to a position that does not have an executable statement, add the NULL statement.

    DECLARE
       done  BOOLEAN;
    BEGIN
       FOR i IN 1..50 LOOP
          IF done THEN
             GOTO end_loop;
          END IF;
          <<end_loop>>  -- not allowed unless an executable statement follows
          NULL; -- add NULL statement to avoid error
       END LOOP;  -- raises an error without the previous NULL
    END;
    /
    
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    openGauss 2024-05-30 00:44:48
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