mysql 流程控制什么

DELIMITER //

CREATE PROCEDURE CheckGrade(IN score INT)
BEGIN
    IF score >= 90 THEN
        SELECT 'A';
    ELSEIF score >= 80 THEN
        SELECT 'B';
    ELSEIF score >= 70 THEN
        SELECT 'C';
    ELSE
        SELECT 'D';
    END IF;
END //

DELIMITER ;

DELIMITER //

CREATE PROCEDURE CheckGrade(IN score INT)
BEGIN
    CASE 
        WHEN score >= 90 THEN
            SELECT 'A';
        WHEN score >= 80 THEN
            SELECT 'B';
        WHEN score >= 70 THEN
            SELECT 'C';
        ELSE
            SELECT 'D';
    END CASE;
END //

DELIMITER ;

DELIMITER //

CREATE PROCEDURE Counter()
BEGIN
    DECLARE counter INT DEFAULT 0;
    
    loop_label: LOOP
        SET counter = counter + 1;
        IF counter > 10 THEN
            LEAVE loop_label;
        END IF;
        SELECT counter;
    END LOOP loop_label;
END //

DELIMITER ;

DELIMITER //

CREATE PROCEDURE Counter()
BEGIN
    DECLARE counter INT DEFAULT 0;
    
    WHILE counter <= 10 DO
        SET counter = counter + 1;
        SELECT counter;
    END WHILE;
END //

DELIMITER ;

DELIMITER //

CREATE PROCEDURE Counter()
BEGIN
    DECLARE counter INT DEFAULT 0;
    
    REPEAT
        SET counter = counter + 1;
        SELECT counter;
    UNTIL counter > 10 END REPEAT;
END //

DELIMITER ;