SQL更新计数

Question

我有这个table

A B
1 1H
2 1H
1 1G
1 1E

我需要更新此 table 列 A，将 max(a) 按 B 分组，计数 (*) = 2。

结果将是这样的：

A B
2 1H
2 1H
1 1G
1 1E

Answer 1

也许吧？

update tablename t1
set A = (select max(A) from tablename t2 where t2.B = t1.B)
where B in (select B from tablename group by B having count(*) >= 2)

Answer 2

你可以试试下面

update tablename t1
set A = (select count(*) from tablename t2 where t2.B = t1.B having count(*)=2)

SQL UPDATE with having count