SQL SERVER UPDATE的赋值次序

1) 先变量再字段

SET NOCOUNT ON;

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

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

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

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

SET NOCOUNT OFF;结果:Id1 Id2 ----------- ----------- 213243

Id1 Id2 ----------- ----------- 211312413

2) 变量之间, 从左到右

SET NOCOUNT ON;

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

INSERT @Table(Id1, Id2)SELECT 1, 10;

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

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

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

SELECT @i = 1, @j = 0UPDATE @Table SET @i = @j, @j = @iPRINT '@i = ' + 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, 10UNION ALLSELECT 2, 20UNION ALLSELECT 3, 30;

UPDATE @Table SET Id1 = Id2, Id2 = Id1SELECT * FROM @Table

SET NOCOUNT OFF;结果:Id1 Id2 ----------- ----------- 10; 120; 230; 3