G
ggwen
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GUEST, unregistred user!
Oracel书上在讲到用外连接代替‘Not in’时有个例子(说这样可以加快查询速度)
select A.Name,Loding
from Worker A
where A.Name not in
(Select Name from WorekerSkill where Skill='SMITHY')
select A.Name,Lodging
from Worker A,Workersskill b
where A.Name=B.Name(+)
and B.Name is null
and B.Skill(+)='SMITHY'
我想知道第二个SQL语句,where后面条件的执行顺序,是从前往后,
还是从后往前,还是有编译器分析决定?
为了提高查询效率,where后面条件的书写应遵循什么原则?把苛刻条件往前放,还是往后放?
First,Thanks very much!
select A.Name,Loding
from Worker A
where A.Name not in
(Select Name from WorekerSkill where Skill='SMITHY')
select A.Name,Lodging
from Worker A,Workersskill b
where A.Name=B.Name(+)
and B.Name is null
and B.Skill(+)='SMITHY'
我想知道第二个SQL语句,where后面条件的执行顺序,是从前往后,
还是从后往前,还是有编译器分析决定?
为了提高查询效率,where后面条件的书写应遵循什么原则?把苛刻条件往前放,还是往后放?
First,Thanks very much!