mysql將一行變成多行的方法：1、將一行變成多行，代碼為【substring_index(substring_index( a.rn,',',b.help_topic_id + 1 ),',' ,- 1)】；2、將多列變成多行。

mysql將一行變成多行的方法：

把

轉(zhuǎn)成

SELECT     substring_index(substring_index( a.rn,',',b.help_topic_id + 1    ),',' ,- 1) AS rn FROM     (select '1,2,3,4' as rn) a   JOIN mysql.help_topic b ON b.help_topic_id < (length(a.rn) - length( replace(a.rn, ',', '')  ) + 1)

圖A轉(zhuǎn)成圖B

圖a

圖b

SELECT     substring_index(substring_index( a.rn,',',b.help_topic_id + 1    ),  ',' ,- 1    ) AS rn FROM     (select SUBSTR(GROUP_CONCAT( REPEAT(CONCAT(number,','),fre) SEPARATOR ''),1,LENGTH(GROUP_CONCAT( REPEAT(CONCAT(number,','),fre) SEPARATOR ''))-1) as rn  from numbers ) a   JOIN mysql.help_topic b ON b.help_topic_id < (length(a.rn) - length( replace(a.rn, ',', '')  ) + 1)