MySQL中的数据转换

我可以把它降到一行,但是要用额外的逗号:-(

select ID1, 
       group_concat( if( `Type` = 'A', ID2, '') ) A, 
       group_concat( if( `Type` = 'B', ID2, '') ) B
from tab
group by ID1

给予:

+------+------+------+
| ID1  | A    | B    |
+------+------+------+
| 1    | x,y, | ,,z  |
+------+------+------+

提供NULL而不是“”可修复此问题:

select ID1, 
       group_concat( if( `Type`='A', ID2, NULL)) A, 
       group_concat( if(`Type`='B', ID2, NULL)) B
from tab
group by ID1;

给予:

+------+------+------+
| ID1  | A    | B    |
+------+------+------+
| 1    | x,y  | z    |
+------+------+------+