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HomeDatabaseMysql TutorialOracle中容易被忽略的地方

在我们写SQL语句时,我们有时候往往会忽略一些细节,下面是我通过自己动手操作和查阅资料总结出来的,如果有不对的地方,或者有补

在我们写SQL语句时,我们有时候往往会忽略一些细节,下面是我通过自己动手操作和查阅资料总结出来的,如果有不对的地方,或者有补充的,希望给我回复,大家互相学习。谢谢!

1、在进行全表扫描,而全表扫描的表的记录数超过100条,需要建立相应的索引或者更改查询条件,,使用索引查询,避免全表扫描。

2、在查询中,使用到like语句,尽量使用后模糊查询。例如:
select * from tablename where column_name like '%name%' --不会使用column_name上的索引

Oracle中容易被忽略的地方



select * from tablename where column_name like 'name%' --使用column_name上的索引

Oracle中容易被忽略的地方



3、如果in后面的子查询或者列表超过5个值,尽量不要使用in,而使用exists;使用not exists,而不使用not in.

4、无用的字段不要select出来。

更多Oracle相关信息见Oracle 专题页面 ?tid=12

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