如何查询三个表中是否存在“用户名”(三个表的“用户名”字段都不一样)。就是会员注册的时候判断一下用户名是否在三个表中存在下面的语法都是返回 0SELECT @TempID = count(1) FROM ny_daili a, ny_huiyuan b, ny_zongguanli c WHERE a.dl_dengluming=@dl_dengluming or b.hy_huiyuanming=@dl_dengluming or c.gl_guanliming=@dl_dengluming
IF @TempID = 0
IF @TempID = 0
FROM ny_daili
WHERE dl_dengluming=@dl_dengluming
)+(select count(1)
from ny_huiyuan
where hy_huiyuanming=@dl_dengluming
)+(select count(1)
from ny_zongguanli
where gl_guanliming=@dl_dengluming
)IF @TempID = 0
(
select cnt = count(*) from tb1 where 用户名 = '某值'
union all
select cnt = count(*) from tb2 where 用户名 = '某值'
union all
select cnt = count(*) from tb3 where 用户名 = '某值'
) t
from
(select dl_dengluming as dl_dengluming from ny_daili
union
select hy_huiyuanmin from ny_huiyuan
union
select gl_guanliming from ny_zongguanli) t where dl_dengluming=@dl_dengluming