SQL 多个 table 条件查询

Question

使用 MySQL，我想在一次插入中完成所有这些操作：

table T1 contains column Ca & Cb. T1 is in database D1. Insert into table T1 specifying column Ca, Cb.

table T2 contains column C2. T2 is in database D2. Set T1.Ca's value with T2.C2

table T3 contains column C3 & C4. T3 is in database D2. use the T2.C2 value to query T3.C3 and use the C4 value of the same row to set T1.Cb

所以我做到了：

insert into T1(Ca, Cb)
select C2
from D2.T2
union
select C4
from D2.T3
where C3=T2.C2;

错误代码：1054。'where clause'

中的未知列 'T2.C2'

请帮忙。提前谢谢你。

Answer 1

合并的查询彼此独立。
你想加入这些表。

select C2,C4
from D2.T2 a
INNER JOIN  D2.T3 b  ON b.C3=a.C2;

Answer 2

如果我理解正确，你应该使用连接而不是联合

   insert into D1.T1(Ca, Cb)
   select T2.C2, T3.C4
   from D2.T2 
   INNER JOIN D2.T3 on T2.C2 = T3.C3

工会的第二个select不知道第一个select的内容..所以你有错误

Unknown column 'T2.C2' in 'where clause'

SQL 多个 table 条件查询

SQL query from multiple table with condition

mysql

sql

union