如何使用MyISAM表针对使用MySQL的MySQL加快使用两次相同表的查询的速度？

Question

I use a query like the following that use twice the same table utdat in order to recover the data.

The key that link together the 2 table is tableA.utprog = tableB.utprog.

SELECT tableA.upd, tableB.utdata  FROM utdat as tableA, utdat AS tableB 
WHERE tableA.uttdat = 'I' AND tableA.utctip = '01' AND   
substring(tableA.utreco, 1, 1) = '3' 
AND tableB.uttdat = 'I' AND tableB.utctip = '01' AND 
substring(tableB.utreco, 1, 1) = '1' 
AND tableA.utprog = tableB.utprog AND TRIM(substr(tableB.utreco, 65, 
12)) = '20000190';

There is a way to speed up this query on MyISAM db ?

Answer 1

Create a multi-column index on the 3 columns used in the WHERE clause:

ALTER TABLE utdat ADD INDEX (uttdat, utctip, itreco);

And change SUBSTRING(tableA.utreco, 1, 1) = 3 to tableA.utreco LIKE '3%', as MySQL knows how to optimize prefix matching in a LIKE expression, but it may not realize that SUBSTR` is extracting a prefix.

it won't affect performance, but you should also learn ANSI JOIN syntax.

SELECT tableA.upd, tableB.utdata  
FROM utdat as tableA
JOIN utdat AS tableB ON tableA.utprog = tableB.utprog
WHERE tableA.uttdat = 'I' AND tableA.utctip = '01' AND tableA.utreco LIKE '3%' 
AND tableB.uttdat = 'I' AND tableB.utctip = '01' AND tableB.utreco LIKE '1%' 
AND TRIM(substr(tableB.utreco, 65, 12)) = '20000190';