Substring ignores index
Posted by:
Matt Ryan
Date: September 29, 2006 08:59AM
Not sure if this is a bug or a "feature"
this query hits the don index, 14 char normal index
select * from cbcom where don LIKE 'W919AK%'
this query does not
select * from cbcom where substring(don,1,6)='W919AK'
the problem is I'm trying to do a join on another table
explain
select b.* from afghanistan_dodaac a inner join cbcom b
on a.dodaac = substring_index(b.don,1,6)
no indexes are hit, it runs 30 minutes,
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE b ALL 15,128,943
1 SIMPLE a ref DODAAC DODAAC 6 func 1 Using where; Using index
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Substring ignores index
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September 29, 2006 08:59AM
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