table 1:
pk1 pk2 pk3 field1 field2 modifieddate version
table 2:
pk1 pk3 tab1 tab2 tab3
(pk1,pk2)-primary key for table1 (pk1,pk3)-primary key for table2
pk1,pk3 -foreign key
The sample query is like this:
select *.tab1, tab2.field1
from table1 tab1
LEFT JOIN table2 tab2
ON (tab1.pk1 =tab2.pk1 AND tab1.pk3 = tab2.pk3)
WHERE (tab1.pk1= 'xx' OR tab1.pk1 = 'yy')
AND (tab1.pk3 = 'aa' OR tab1.pk3 is null)
AND (tab1.modifieddate >'somevalue' OR (tab1.modifieddate = 'somevalue' AND tab1.pk2 > ' \n') )
AND tab1.field1 = (select max(field1) from table1
where ((tab1.pk1= 'xx' OR tab1.pk1 = 'yy')
AND (tab1.pk3 = 'aa' OR tab1.pk3 is null) AND field3 = tab1.field3))
ORDER BY modifieddate desc,pk1 desc
limit 0,50
The indexes created are:
index1(pk1,pk3,modifieddate,pk2,field3)
index2(pk1,modifieddate,pk2,field3)
foreignkeyindex(pk1,pk3)
subqueryindex(pk1,pk3,field2)
As I analyzed, I found that using OR in the outer query is the reason for not taking up index. http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html-- > last comment by Stephen Dewey.
I gone through many posts of stackoverflow and tried using UNION ALL. In that case, for my scenario, I ended up with a derived table. Can a derived table be made to use the indexes?
EDIT Explain plan:
id select-type table type possible_keys key key-len ref rows extra
1 primary tab1 range primary,index1,index2 pk3 497 null 734 using where;using filesort
2 primary tab2 ref primary,forignkeyindex,pk3 pk3 110 db.tab1.pk3 1
3 dependent subquery table1 ref_or_null pk3,subqueryindex subqueryindex 497 tab1.pk3,tab1.field1 2 using where
Would you please give some help on optimizing this query? :)
You join using
tab1.pk1 =tab2.pk1 AND tab1.pk3 = tab2.pk3)
try creating an index with the keys you use to join, ie
table1: index1(pk1,pk3)
table2: index2(pk1,pk3)
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