如何在MySQL中的单个列中删除重复的逗号分隔值

Question

SELECT id, country FROM my_records

我从MySQL查询得到了上述结果,我想从结果中删除重复的ID.不是在PHP代码的帮助下,而是使用MySQL查询.是否有任何功能或查询来做同样的事情.

谢谢

Answer 1

我陷入了类似的情况,发现MySql没有提供任何预定义的功能来克服这个问题.

为了克服我创建了一个UDF,请看下面的定义和用法.

DROP FUNCTION IF EXISTS `get_unique_items`;
DELIMITER //
CREATE FUNCTION `get_unique_items`(str varchar(1000)) RETURNS varchar(1000) CHARSET utf8
BEGIN

        SET @String      = str;
        SET @Occurrences = LENGTH(@String) - LENGTH(REPLACE(@String, ',', ''));
        SET @ret='';
        myloop: WHILE (@Occurrences > 0)
        DO 
            SET @myValue = SUBSTRING_INDEX(@String, ',', 1);
            IF (TRIM(@myValue) != '') THEN
                IF((LENGTH(@ret) - LENGTH(REPLACE(@ret, @myValue, '')))=0) THEN
                        SELECT CONCAT(@ret,@myValue,',') INTO @ret;
                END if;
            END IF;
            SET @Occurrences = LENGTH(@String) - LENGTH(REPLACE(@String, ',', ''));
            IF (@occurrences = 0) THEN 
                LEAVE myloop; 
            END IF;
            SET @String = SUBSTRING(@String,LENGTH(SUBSTRING_INDEX(@String, ',', 1))+2);
        END WHILE;    
SET @ret=concat(substring(@ret,1,length(@ret)-1), '');
return @ret;

END //
DELIMITER ;

样品用法:

SELECT get_unique_items('2,2,2,22,2,3,3,3,34,34,,54,5,45,,65,6,5,,67,6,,34,34,2,3,23,2,32,,3,2,,323') AS 'Items';

结果:

2,22,3,34,54,45,65,67,23,32,323

希望这有帮助!