请问能否写出带主键的SQL语句。
下面是我的SQL语句
select * from
(select a,b,c from tab1 union
select d,e,f from tab2 union
select g,h,i from tab3) tab
where a='**'
下面是我的SQL语句
select * from
(select a,b,c from tab1 union
select d,e,f from tab2 union
select g,h,i from tab3) tab
where a='**'
(select a,b,c from tab1 union
select d,e,f from tab2 union
select g,h,i from tab3) tab
where a='**'
order by a --LZ是想要加排序字段?????
MAPINFO里面的SQL语句必须是要有唯一键的我现在要查询的东西必须UNION多个表,但是UNION的时候是没有唯一键的能否写一个带唯一键的SQL语句
from ....
?????
至于要把几个表做成一个表由于实时性太强,效率将很低