具有多个记录的MySQL CREATE FUNCTION结果给出错误＃1172

Question

I have the following 3 tables:

table "name"       
---------------
id     name
---------------
1      book
2      pen


table "color"
------------------
id     color
------------------
1       red
2       yello
3       green
4       pink


table "both"
------------------------
id     name      color
----------------------
1      1            1
2      1            2
3      1            3
4      2            2

and I have the following function:

    DELIMITER //

    CREATE FUNCTION get_word(n VARCHAR(20))
        RETURNS VARCHAR(10)
        READS SQL DATA
        DETERMINISTIC
        BEGIN
            DECLARE b VARCHAR(20);
       SELECT  `color`.`color` INTO b  FROM   `name` 
        LEFT JOIN `both` 
          ON `name`.`id`=`both`.`name`
        LEFT JOIN `color`
          ON `color`.`id`=`both`.`color` 
       WHERE `name`.`name`=n;        

        RETURN b;
        END//

    DELIMITER ;

now when I run SELECT get_word('pen') it returns yellow which is what is expect.

but when I run the code SELECT get_word('book') it get error: #1172 - Result consisted of more than one row

my Question: What to do so this function works with multiple records as well as single record which it does when I search for "pen"? thanks

UPDATE:

If use the query without the function as follow, it just works fine:

       SELECT  `color`.`color` AS b  FROM   `name` 
        LEFT JOIN `both` 
          ON `name`.`id`=`both`.`name`
        LEFT JOIN `color`
          ON `color`.`id`=`both`.`color` 
       WHERE `name`.`name`='book'; 

and it returns:

**b**
red
yellow
green

Answer 1

Well, it seems that you want a resultset (more than one value)

But a mysql stored function cannot return a resultset (see doc : Restrictions for Stored Functions).

Solution 1 : use a stored procedure

CREATE PROCEDURE get_word(n VARCHAR(20))
BEGIN
 SELECT  `color`.`color` 
 FROM   `name` 
   LEFT JOIN `both` 
          ON `name`.`id`=`both`.`name`
   LEFT JOIN `color`
          ON `color`.`id`=`both`.`color` 
   WHERE `name`.`name`=n; 
END

Solution2 : return a concatenated string

something like "green, yellow, blue" GROUP_CONCAT can do that easily. see this stackoverflow question for example

Answer 2

尝试在where之后使用group by，例如，尝试group by id或表中唯一的内容添加group by id 。