mysql怎么用循环

DELIMITER //

CREATE PROCEDURE simple_loop()
BEGIN
    DECLARE counter INT DEFAULT 1;
    
    WHILE counter <= 5 DO
        SELECT counter;
        SET counter = counter + 1;
    END WHILE;
END //

DELIMITER ;

CALL simple_loop();

DELIMITER //

CREATE PROCEDURE repeat_loop()
BEGIN
    DECLARE counter INT DEFAULT 1;
    
    REPEAT
        SELECT counter;
        SET counter = counter + 1;
    UNTIL counter > 5 END REPEAT;
END //

DELIMITER ;

CALL repeat_loop();

DELIMITER //

CREATE PROCEDURE loop_example()
BEGIN
    DECLARE counter INT DEFAULT 1;
    
    loop_label: LOOP
        SELECT counter;
        SET counter = counter + 1;
        
        IF counter > 5 THEN
            LEAVE loop_label;
        END IF;
    END LOOP loop_label;
END //

DELIMITER ;

CALL loop_example();

DELIMITER //

CREATE PROCEDURE cursor_example()
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE counter INT;
    DECLARE cur CURSOR FOR SELECT id FROM your_table;
    
    OPEN cur;
    
    read_loop: LOOP
        FETCH cur INTO counter;
        
        IF done THEN
            LEAVE read_loop;
        END IF;
        
        SELECT counter;
    END LOOP;
    
    CLOSE cur;
END //

DELIMITER ;

CALL cursor_example();

DELIMITER //

CREATE PROCEDURE avoid_infinite_loop()
BEGIN
    DECLARE counter INT DEFAULT 1;
    
    WHILE counter <= 5 DO
        SELECT counter;
        SET counter = counter + 1;
    END WHILE;
END //

DELIMITER ;

CALL avoid_infinite_loop();