t1
-----------------------
id A B C
t2
---------------------
id F
如果满足条件：t1.id = t2.id , t1.B = '0 '， F = null
就把F的值设置为C
请问如何实现 ？
------解决方案--------------------
Update t2 set F=(Select C from t1 where t1.id=t2.id and t1.B = '0 ')
where F is null
------解决方案--------------------
update t2 ta set F=(select c from t1 tb where ta.id = tb.id and tb.B = 0
and exists(select 'X ' from t2 where ta.id = id and tb.B = '0 ' and F is null));
------解决方案--------------------
update t2 t_2
set t_2.F = 'C '
where exists (
select 1
from t1 t_1
where t_1.id = t_2.id
and t_1.B = '0 '
and t_2.F is null
);
试试看~~