mysql 判断执行语句怎么写

DELIMITER //

CREATE PROCEDURE CheckUser(IN userId INT)
BEGIN
    DECLARE userCount INT;

    SELECT COUNT(*) INTO userCount FROM users WHERE id = userId;

    IF userCount > 0 THEN
        SELECT 'User exists';
    ELSE
        SELECT 'User does not exist';
    END IF;
END //

DELIMITER ;

SELECT 
    id,
    name,
    CASE 
        WHEN age < 18 THEN 'Minor'
        WHEN age BETWEEN 18 AND 65 THEN 'Adult'
        ELSE 'Senior'
    END AS age_group
FROM users;

SELECT 
    id,
    name,
    IFNULL(phone_number, 'N/A') AS phone_number
FROM users;

DELIMITER //

CREATE PROCEDURE UpdateUser(IN userId INT, IN newName VARCHAR(255))
BEGIN
    DECLARE userExists INT;

    SELECT COUNT(*) INTO userExists FROM users WHERE id = userId;

    IF userExists > 0 THEN
        UPDATE users SET name = newName WHERE id = userId;
        SELECT 'User updated successfully';
    ELSE
        SELECT 'User does not exist';
    END IF;
END //

DELIMITER ;