SQL SERVER UPDATE的赋值次序

SQL SERVER UPDATE的赋值次序2007-05-311）先变量再字段

SET NOCOUNT ON;

DECLARE @i INT, @j INT
DECLARE @Table TABLE
（
Id1 INT,
Id2 INT
）;

INSERT @Table（Id1, Id2）
SELECT 1, 10
UNION ALL
SELECT 2, 20
UNION ALL
SELECT 3, 30;

SELECT @i = 1, @j = 0
UPDATE @Table SET Id1 = @i, Id2 = Id1, @i = @i + 1
SELECT * FROM @Table

SELECT @i = 1, @j = 0
UPDATE @Table SET Id1 = @i, Id2 = @j, @j = @i + 10, @i = @i + 1
SELECT * FROM @Table

SET NOCOUNT OFF;
结果:
Id1 Id2
----------- -----------
2 1
3 2
4 3

Id1 Id2
----------- -----------
2 11
3 12
4 13

2）变量之间, 从左到右

SET NOCOUNT ON;

DECLARE @i INT, @j INT
DECLARE @Table TABLE
（
Id1 INT,
Id2 INT
）;

INSERT @Table（Id1, Id2）
SELECT 1, 10;

SELECT @i = 1, @j = 0
UPDATE @Table SET @j = @i, @i = @i + 1
PRINT= " + CAST（@i AS VARCHAR） + ", @j = " + CAST（@j AS VARCHAR）

SELECT @i = 1, @j = 0
UPDATE @Table SET @i = @i + 1, @j = @i
PRINT= " + CAST（@i AS VARCHAR） + ", @j = " + CAST（@j AS VARCHAR）

SELECT @i = 1, @j = 0
UPDATE @Table SET @i = @j + 1, @j = @i
PRINT= " + CAST（@i AS VARCHAR） + ", @j = " + CAST（@j AS VARCHAR）

SELECT @i = 1, @j = 0
UPDATE @Table SET @i = @j, @j = @i
PRINT= " + CAST（@i AS VARCHAR） + ", @j = " + CAST（@j AS VARCHAR）

SET NOCOUNT OFF;
结果:
@i = 2, @j = 1
@i = 2, @j = 2
@i = 1, @j = 1
@i = 0, @j = 0

3）字段之间, 并行执行

SET NOCOUNT ON;

DECLARE @Table TABLE
（
Id1 INT, Id2 INT
）;

INSERT @Table（Id1, Id2）
SELECT 1, 10
UNION ALL
SELECT 2, 20
UNION ALL
SELECT 3, 30;

UPDATE @Table SET Id1 = Id2, Id2 = Id1
SELECT * FROM @Table

SET NOCOUNT OFF;
结果:
Id1 Id2
----------- -----------
10 1
20 2
30 3