Optimize query mysql - mysql

Question

i have a problem with a query for a web site. This is the situation:
I have 3 table:
articoli = where there are all article
clasart = where there are all the matches between the code article and class code - 32314 rows
classificazioni = where there are all matches between class code and name of class - 2401 rows
and this is the query
SELECT a.clar_classi , b.CLA_DESCRI
FROM clasart a JOIN (
SELECT art.AI_CAPOCODI, art.ai_codirest
FROM (select * from clasart where clar_azienda = 'SRL') a
JOIN (
SELECT AI_CAPOCODI, AI_CODIREST,AI_DT_CREAZ,
AI_DESCRIZI, AI_CATEMERC, concat(AI_CAPOCODI, AI_CODIREST) as codice, aI_grupscon
FROM articoli
WHERE AI_AZIENDA = 'SRL' AND AI_CATEMERC LIKE '0101______' AND AI_FLAG_NOW = 0 AND AI_CAPOCODI <> 'zzz'
) art ON trim(a.CLAR_ARTICO) = art.AI_CODIREST
JOIN classificazioni b ON a.CLAR_CLASSI = b.CLA_CODICE
WHERE b.CLA_CODICE LIKE 'AA51__'
group by CLAR_ARTICO) art ON trim(CLAR_ARTICO) = concat(art.AI_CAPOCODI, art.ai_codirest)
JOIN classificazioni b ON a.CLAR_CLASSI = b.CLA_CODICE
WHERE CLAR_AZIENDA = 'SRL' AND CLAR_CLASSI like 'CO____'
The time of run is 16 second. The time increase to 16 second when join with classificazioni.
You can help me? Thanks

Answer 1

Introduce following indexing using the queries below and after that the query will start running within a second or two:
ALTER TABLE articoli ADD INDEX idx_artc_az_cat_flg_cap (AI_AZIENDA, AI_FLAG_NOW, AI_CAPOCODI, AI_CATEMERC);
The above query will introduce the multi-column indexes on articoli table. The indexing work similar way how hash tables or keys of the array work to directly identifying the row on which the target value(s) match. Using multi-column will result in comparison of less number of rows.
Do not use trim(a.CLAR_ARTICO): make sure that before insertion the values are trimmed but not at the time of joining. This can result in skipping the index files and the join comparison can be expensive this way.
Let's move to next steps:
Introduce index on clar_azienda using following query:
ALTER TABLE clasart ADD INDEX idx_cls_az (clar_azienda);
If art.AI_CODIREST is not a primary/foreign key you'll need to introduce index there using the query below:
ALTER TABLE classificazioni ADD INDEX idx_clsi_cd (CLA_CODICE);
We are almost done, you'll just need to index CLAR_AZIENDA as well the same way how I indexed the above columns. Let me also tell you what is what in index column last query so you can write your own.
ALTER TABLE <tableName> ADD INDEX <indexKey (<column to be indexed>);
Let me know if you still have issues, remember you can run these queries after selecting your database from PhpMyAdmin (SQL tabl) or on mysql console.