SQL优化: 匹配中间字段内容的一种写法
作者:互联网
众所周知,当索引字段使用like时,只有前缀查找才会走索引,但难免有时候需要匹配字符串中间部分内容,如果这个时候,选择字段只有索引字段,会走索引,例如:
例: select tob.object_name from test_objects tob
where tob.object_name like '%EFGHI%';
注: object_name 有索引
SELECT STATEMENT, GOAL = ALL_ROWS 105 2745 107055
INDEX FAST FULL SCAN LOTPYTHON IND_TEST_OBJECTS001 105 2745 107055
但如果选择内容包含非索引字段时,是不会走索引的。
例:select tob.object_name,tob.object_id from test_objects tob
where tob.object_name like '%EFGHI%'
注: object_name 有索引
SELECT STATEMENT, GOAL = ALL_ROWS 307 2745 120780
TABLE ACCESS FULL LOTPYTHON TEST_OBJECTS 307 2745 120780
那有没有好的办法呢,其实还是可以通过某种写法规避的。
例如:with test_like as (select object_name from test_objects
where object_name like '%EFGHI%'
union all
select '不可能出现的词' as object_name from dual
)
select tob.object_name,tob.object_id from test_objects tob
where tob.object_name in (select * from test_like);
SELECT STATEMENT, GOAL = ALL_ROWS 112 1 110
HASH JOIN 112 1 110
NESTED LOOPS 112 1 110
NESTED LOOPS 112 1 110
STATISTICS COLLECTOR
VIEW SYS VW_NSO_1 108 2746 181236
HASH UNIQUE 1 181236
VIEW LOTPYTHON 108 2746 181236
UNION-ALL
INDEX FAST FULL SCAN LOTPYTHON IND_TEST_OBJECTS001 105 2745 107055
FAST DUAL 2 1
INDEX RANGE SCAN LOTPYTHON IND_TEST_OBJECTS001 2 1
TABLE ACCESS BY INDEX ROWID LOTPYTHON TEST_OBJECTS 3 1 44
TABLE ACCESS FULL LOTPYTHON TEST_OBJECTS 3 1 44
该写法有一个限制条件,就是查询返回的数据量不是很大,当然,数据量返回很大的时候,也不应该走索引。
标签:匹配,name,object,索引,test,SQL,tob,LOTPYTHON,写法 来源: https://blog.csdn.net/zhougongping/article/details/123091177