MySQL存储过程基于参数的返回值

Question

I'm trying to create a stored procedure in MySql where it will return all users based on the gender parameter and here is my code:

DELIMITER $$

USE `my_database`$$

DROP PROCEDURE IF EXISTS `GET_ALL_USERS`$$

CREATE DEFINER=`root`@`localhost` PROCEDURE `GET_ALL_USERS`(IN IN_GENDER CHAR)
    COMMENT 'Get All Users'
BEGIN
    SELECT
        *
    FROM
        users
    WHERE
        gender = IN_GENDER;
END$$

DELIMITER;

This code works when the parameter is set to 'f' or 'm'. When the gender param is not set it returns nothing. What i want is if the gender param is not set it will return all users. What value should I set to the gender parameter to get all users? Please help thanks

Answer 1

Off the top of my head, not tested...

Try it like this:

gender LIKE CASE WHEN IN_GENDER='' THEN '%' ELSE IN_GENDER END AS MOD_IN_GENDER;

or like this:

gender LIKE COALESCE(IN_GENDER, '%')