mysql - 如何在子查询中使用 in 子句

Question

我有如下两张表，

表 1:

ID      NAME    
------  --------
IM-1    Pencil  
IM-2    Pen     
IM-3    NoteBook
IM-4    Eraser  

表 2:

ID      ITEM_ID       
------  --------------
MT-1    IM-1          
MT-2    IM-1,IM-2,IM-3     
MT-3    IM-1,IM-2,IM-4

要求的结果是:

ID      ITEMNAME
------  --------
MT-1    Pencil  
MT-2    Pencil,Pen,NoteBook  
MT-3    Pencil,Pen,Eraser  

但是通过使用查询

---

SELECT T2.ID, 
          (SELECT T1.NAME 
           FROM TABLE1 AS T1 
           WHERE T1.ID IN (T2.ITEM_ID)) AS ITEMNAME 
    FROM TABLE2 AS T2

我得到结果:

---

ID      ITEMNAME
------  --------
MT-1    Pencil  
MT-2    (NULL)  
MT-3    (NULL)  

谁能帮帮我？

Answer 1

如果不规范化，你可以试试这个。但是这个查询不会是 SARGable，并且作为 ypercube pointed out在数据库中存储逗号分隔列表 is a bad idea .

  SELECT T2.ID,
         GROUP_CONCAT(T1.NAME SEPARATOR  ',')
   FROM TABLE2 AS T2
        INNER JOIN  TABLE2 AS T1
        ON FIND_IN_SET (T1.ID , T2.ITEM_ID )
   GROUP BY 
         T2.ID