SQL SERVER中WHERE语句的执行顺序是怎么样的

Question

逻辑上：
T1.USER_ID = T2.USER_ID
T1.USER_ID = 'aaaaa'

Answer 1

先T1.USER_ID = T2.USER_ID
后T1.USER_ID = 'aaaaa'当然,SQL会自动去选择先执行哪个.

Answer 2

先T1.USER_ID = 'aaaaa'  后T1.USER_ID = T2.USER_ID 

Answer 3

貌似05里面已经优化了???set showplan_all on
goselect * from T1,T2
where  T1.id = T2.id and T1.id =1
/*
select * from T1,T2
where  T1.id = T2.id and T1.id =1                                
  |--Nested Loops(Inner Join)                                                         
       |--Table Scan(OBJECT:([CSDN].[dbo].[T2]), WHERE:([CSDN].[dbo].[T2].[id]=(1)))  
       |--Table Scan(OBJECT:([CSDN].[dbo].[T1]), WHERE:([CSDN].[dbo].[T1].[id]=(1)))
*/

Answer 4

肯定是先T1.USER_ID = 'aaaaa' 然后再T1.USER_ID = T2.USER_ID