In my company we use a commercial software running with mysql 5.5 (MyISAM) that often executes a query of this form:
SELECT table1.attrib1 FROM table2, table1 WHERE table2.status = 'Active' AND table2.table1 = CONCAT( 'constant prefix', table1.attrib1 )
The output of
EXAMINE tells me that the index on
table2.table1 is used, but the index on
table1.attrib1 isn't used to execute the query. Instead all existing rows of
table1 are accessed (full table scan). The expected result contains only a few rows.
It's a commercial software, so I can't change the query. But I could add indexes or change database parameters.
Question: What can I do to speed up this query?