我有这样的表:
_id| letter| extra
1 | A | some
2 | A | another
3 | A | information
4 | B | NULL
5 | B | 98090
当 LETTER 更改时,我需要区分第一行:
_id| letter| extra | mediator
1 | A | some | 1
2 | A | another |
3 | A | information |
4 | B | NULL | 1
5 | B | 98090 |
或者 ...
_id| letter| extra | count
1 | A | some | 1
2 | A | another | 2
3 | A | information | 3
4 | B | NULL | 1
5 | B | 98090 | 2
(在这种情况下,我知道我需要 count = 1)