Help Center/ GaussDB/ Developer Guide(Distributed_3.x)/ Stored Procedures/ Control Statements/ Loop Statements
Updated on 2024-05-07 GMT+08:00
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Loop Statements

Simple LOOP Statements

Syntax diagram

Figure 1 loop::=

Example

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CREATE OR REPLACE PROCEDURE proc_loop(i in integer, count out integer) 
AS 
    BEGIN 
        count:=0; 
        LOOP 
        IF count > i THEN 
            raise info 'count is %. ', count;  
            EXIT; 
        ELSE 
            count:=count+1; 
        END IF; 
        END LOOP; 
    END;
/

CALL proc_loop(10,5);

The loop must be exploited together with EXIT; otherwise, a dead loop occurs.

WHILE_LOOP Statements

Syntax diagram

Figure 2 while_loop::=

If the conditional expression is true, a series of statements in the WHILE statement are repeatedly executed and the condition is decided each time the loop body is executed.

Example

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CREATE TABLE integertable(c1 integer) DISTRIBUTE BY hash(c1); 
CREATE OR REPLACE PROCEDURE proc_while_loop(maxval in integer) 
AS 
    DECLARE 
    i int :=1;  
    BEGIN 
        WHILE i < maxval LOOP 
            INSERT INTO integertable VALUES(i); 
            i:=i+1; 
        END LOOP; 
    END; 
/

-- Invoke a function.
CALL proc_while_loop(10);

-- Delete the stored procedure and table.
DROP PROCEDURE proc_while_loop;
DROP TABLE integertable;

FOR_LOOP (Integer variable) Statement

Syntax diagram

Figure 3 for_loop::=
  • The variable name is automatically defined as the integer type and exists only in this loop. The variable name falls between lower_bound and upper_bound.
  • When the keyword REVERSE is used, the lower bound must be greater than or equal to the upper bound; otherwise, the loop body is not executed.

Example

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-- Loop from 0 to 5.
CREATE OR REPLACE PROCEDURE proc_for_loop()
AS
    BEGIN
    FOR I IN 0..5 LOOP
        DBE_OUTPUT.PRINT_LINE('It is '||to_char(I) || ' time;') ;
    END LOOP;
END;
/

-- Invoke a function.
CALL proc_for_loop();

-- Delete the stored procedure.
DROP PROCEDURE proc_for_loop;

FOR_LOOP Query Statements

Syntax diagram

Figure 4 for_loop_query::=

The variable target is automatically defined, its type is the same as that in the query result, and it is valid only in this loop. The target value is the query result.

Example

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-- Display the query result from the loop.
CREATE OR REPLACE PROCEDURE proc_for_loop_query()
AS 
    record VARCHAR2(50);
BEGIN 
    FOR record IN SELECT spcname FROM pg_tablespace LOOP 
    dbe_output.print_line(record); 
    END LOOP; 
END; 
/

-- Invoke a function.
CALL proc_for_loop_query();

-- Delete the stored procedure.
DROP PROCEDURE proc_for_loop_query;

FORALL Batch Query Statements

Syntax diagram

Figure 5 forall::=

The variable index is automatically defined as the integer type and exists only in this loop. The index value falls between low_bound and upper_bound.

Example

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CREATE TABLE TEST_t1 (
  title NUMBER(6),
  did VARCHAR2(20),
  data_period VARCHAR2(25),
  kind VARCHAR2(25),
  interval VARCHAR2(20),
  time DATE,
  isModified VARCHAR2(10)
)
DISTRIBUTE BY hash(did);

INSERT INTO TEST_t1 VALUES( 8, 'Donald', 'OConnell', 'DOCONNEL', '650.507.9833', to_date('21-06-1999', 'dd-mm-yyyy'), 'SH_CLERK' );

CREATE OR REPLACE PROCEDURE proc_forall()
AS 
BEGIN 
    FORALL i IN 100..120 
        update TEST_t1 set title = title + 100*i;
END; 
/

-- Invoke a function.
CALL proc_forall();

-Query the invocation result of the stored procedure.
SELECT * FROM TEST_t1 WHERE title BETWEEN 100 AND 120;

-- Delete the stored procedure and table.
DROP PROCEDURE proc_forall;
DROP TABLE TEST_t1;
Parent topic: Control Statements