使用mysql将逗号分隔值从表列拆分为行？

Question

我找到了post，其中包含3个以逗号分隔的值。我将用逗号分隔3个以上的值。例如，

ID    CITY_ID
--------------
1     12,18,16,17,35
2     12,16
....
--------------

是否可以拆分字符串city_id并使用mysql查询将其分成行，如下所示

  ID   CITY_ID
  -------------
   1    12
   1    18
   1    16
    ....
   2    16
    ....
  --------------

如果是，请提供一些建议......

Answer 1

试试这个

  SELECT ID,SUBSTRING_INDEX(SUBSTRING_INDEX(t.CITY_ID, ',', n.n), ',', -1) value
  FROM Table1 t CROSS JOIN 
  (
   SELECT a.N + b.N * 10 + 1 n
     FROM 
    (SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
   ,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
    ORDER BY n 
   ) n
 WHERE n.n <= 1 + (LENGTH(t.CITY_ID) - LENGTH(REPLACE(t.CITY_ID, ',', '')))
 ORDER BY ID,value

<强> FIDDLE DEMO

输出：

---

ID  VALUE
1   12
1   16
1   17
1   18
1   35
2   12
2   16