类似这样的?SELECT ProductName FROM Northwind.dbo.Products WHERE UnitPrice = (SELECT UnitPrice FROM Northwind.dbo.Products WHERE ProductName = 'Sir Rodney''s Scones')
現在有這樣的應用: TabA結構與值如下 -------------------------- A B C D -------------------------- 1 1 1 1 2 2 2 3 1 2 3 2 2 1 3 4 --------------------------- 值只表示填充位 TabB ------------------- A B ---------------- 1 3 2 4 1 5 -------------------當tabb.a 和 tabb.b 等於 Taba.a 和tabb.b 時顯示Taba中的所有列--類似以上的應用怎樣寫查詢?
select a.* from taba a left join tabb b on a.a=b.a and a.b=b.b where b.a is not null
select 1,2,3,2 union all select 2,1,3,4create table tabb ( A int, B int ) insert tabb select 1,1 union all select 2,4 union all select 2,1 select * from taba select * from tabbselect a.* from taba a left join tabb b on a.a=b.a and a.b=b.b where b.a is not nullA B C D ----------- ----------- ----------- ----------- 1 1 1 1 2 1 3 4
FROM Northwind.dbo.Products
WHERE UnitPrice =
(SELECT UnitPrice
FROM Northwind.dbo.Products
WHERE ProductName = 'Sir Rodney''s Scones')
(NOT)EXISTS 子查询能否返回行集
字段=(SELECT ..) 字段=子查询产生的一个值,记住,只有一行一列
常数>(SELECT COUNT(...) ... ) 子查询返回一个INT型数据
TabA結構與值如下
--------------------------
A B C D
--------------------------
1 1 1 1
2 2 2 3
1 2 3 2
2 1 3 4
---------------------------
值只表示填充位
TabB
-------------------
A B
----------------
1 3
2 4
1 5
-------------------當tabb.a 和 tabb.b 等於 Taba.a 和tabb.b 時顯示Taba中的所有列--類似以上的應用怎樣寫查詢?
b.a is not null
select 2,1,3,4create table tabb
(
A int,
B int
)
insert tabb
select 1,1 union all
select 2,4 union all
select 2,1
select * from taba
select * from tabbselect a.* from taba a left join tabb b on a.a=b.a and a.b=b.b where
b.a is not nullA B C D
----------- ----------- ----------- -----------
1 1 1 1
2 1 3 4