[英]How to improve slow query with indexed tables MariaDB?
該查詢平均需要2/3秒。 聯接中的每個字段以及索引在哪里。
我如何改善此查詢?
SELECT DISTINCT pro_id, pro_url, pro_data, pro_capa, pro_destaque, pro_destaque_data, pro_nome, pro_likes, pro_views, pro_comentarios_total, pro_autor FROM projeto JOIN utilizador_projeto ON pro_id=utp_proid JOIN utilizador ON utp_utiid=uti_id WHERE pro_activo=1 AND pro_privacidade=1 ORDER BY pro_destaque_data DESC LIMIT 24;
slow_query_log:
# Time: 190923 1:10:58
# User@Host: root[root] @ [10.133.247.241]
# Thread_id: 36 Schema: db QC_hit: No
# Query_time: 3.575462 Lock_time: 0.000114 Rows_sent: 24 Rows_examined: 104820
# Rows_affected: 0 Bytes_sent: 3974
MariaDB [db]> EXPLAIN SELECT DISTINCT pro_id, pro_url, pro_data, pro_capa, pro_destaque, pro_destaque_data, pro_nome, pro_likes, pro_views, pro_comentarios_total, pro_autor FROM projeto JOIN utilizador_projeto ON pro_id=utp_proid JOIN utilizador ON utp_utiid=uti_id WHERE pro_activo=1 AND pro_privacidade=1 ORDER BY pro_destaque_data DESC LIMIT 24;
+------+-------------+--------------------+--------+-----------------------------------------------------------------------------------------------+---------------------+---------+---------------------------------+-------+------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+--------------------+--------+-----------------------------------------------------------------------------------------------+---------------------+---------+---------------------------------+-------+------------------------------+
| 1 | SIMPLE | projeto | ref | PRIMARY,pro_destaques_index,pro_likes_index,pro_comments_index,pro_views_index,pro_date_index | pro_destaques_index | 2 | const,const | 17865 | Using where; Using temporary |
| 1 | SIMPLE | utilizador_projeto | ref | utp_utiid,utp_proid | utp_proid | 4 | db.projeto.pro_id | 1 | Distinct |
| 1 | SIMPLE | utilizador | eq_ref | PRIMARY | PRIMARY | 4 | db.utilizador_projeto.utp_utiid | 1 | Using index; Distinct |
+------+-------------+--------------------+--------+-----------------------------------------------------------------------------------------------+---------------------+---------+---------------------------------+-------+------------------------------+
WHERE pro_active=1
AND pro_privacy=1
ORDER BY pro_highlight_date DESC
乞求這個“復合”索引:
INDEX(pro_active, pro_privacy, -- in either order
pro_highlight_date)
Rows_examined: 139482
可能會降為Rows_examined: 24
。
假定這3列在同一表中。 請執行以下操作,而不用表名作為列名的前綴:
...
FROM project AS pro
...
WHERE pro.active = 1 ...
這樣就消除了任何歧義(並且擊鍵次數大致相同)。
聯接中的每個字段以及索引在哪里
過度殺傷力。 而且,單列索引通常不如多列(復合)索引有用。 參見: http : //mysql.rjweb.org/doc.php/index_cookbook_mysql
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