如何优化MySQL查询

Question

我有很多查询，如下面的查询。 如何我得到优化他们 -

SELECT DISTINCT 
    n.nid AS nid, n.title AS title, n.created AS created, n.changed AS changed, 
    n.type AS type, n.status AS status, n.uid AS uid, u.name AS name, 
    fit.field_item_topic_tid AS field_item_topic_tid, 
    fui.field_upload_item_fid AS field_upload_item_fid, 
    fist.field_item_sub_topic_tid AS field_item_sub_topic_tid, 
    asid.field_item_asset_id_value AS field_item_asset_id_value, 
    fur.field_item_urgent_value AS field_item_urgent_value, 
    scrubbing.field_item_scrubbing_value AS field_item_scrubbing_value, 
    wsts.field_item_workflow_status_value AS field_item_workflow_status_value, 
    wfs.state AS state 
FROM 
node n 
LEFT OUTER JOIN field_data_field_item_topic fit ON n.nid=fit.entity_id 
LEFT OUTER JOIN field_data_field_upload_item fui ON fui.entity_id= n.nid 
LEFT OUTER JOIN field_data_field_item_sub_topic fist ON n.nid=fist.entity_id 
LEFT OUTER JOIN field_data_field_item_asset_id asid ON n.nid=asid.entity_id 
LEFT OUTER JOIN field_data_field_item_urgent fur ON fur.entity_id= n.nid 
LEFT OUTER JOIN field_data_field_item_scrubbing scrubbing ON scrubbing.entity_id= n.nid 
LEFT OUTER JOIN field_data_field_item_workflow_status wsts ON wsts.entity_id = n.nid 
LEFT OUTER JOIN workflow_states wfs ON wfs.sid = wsts.field_item_workflow_status_value 
LEFT OUTER JOIN users u ON u.uid = n.uid 
WHERE ((n.type = 'item')) 
AND((wsts.field_item_workflow_status_value IN ('All', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10'))) 
AND( (fit.field_item_topic_tid IN ('NULL', '46', '47', '48', '52', '73', '90', '118', '142', '150', '154', '175', '196', '362', '363', '366', '367', '383', '403', '406', '533', '535', '543')) 
    OR (fist.field_item_sub_topic_tid IN ('NULL', '50', '51', '66', '67', '70', '71', '74', '75', '76', '93', '143', '151', '197', '198', '206', '211', '304', '364', '368', '384', '404', '407', '534', '536')) 
) 
ORDER BY n.changed desc 
LIMIT 20 OFFSET 0 

EXPLAIN- 
id select_type  table type possible_keys key  key_len  ref  rows Extra 
1 SIMPLE wsts range entity_id,field_item_workflow_status_value field_item_workflow_status_value 5 NULL 1708 Using where; Using temporary; Using filesort 
1 SIMPLE wfs  eq_ref PRIMARY  PRIMARY  4 lightening1.wsts.field_item_workflow_status_value 1  
1 SIMPLE n eq_ref PRIMARY,node_type,nid PRIMARY  4 lightening1.wsts.entity_id 1 Using where 
1 SIMPLE u eq_ref PRIMARY  PRIMARY  4 lightening1.n.uid 1  
1 SIMPLE fit  ref  entity_id entity_id 4 lightening1.wsts.entity_id 1  
1 SIMPLE fui  ref  entity_id entity_id 4 lightening1.wsts.entity_id 1  
1 SIMPLE fist ref  entity_id entity_id 4 lightening1.n.nid 1 Using where 
1 SIMPLE asid ref  entity_id entity_id 4 lightening1.wsts.entity_id 1  
1 SIMPLE fur  ref  entity_id entity_id 4 lightening1.wsts.entity_id 1  
1 SIMPLE scrubbing ref  entity_id entity_id 4 lightening1.n.nid 1  

Answer 1

您还没有列入表结构（尤其是索引），这样我就可以提供一半的答案。首先注意输出这一行：

1 SIMPLE wsts range entity_id,field_item_workflow_status_value field_item_workflow_status_value 5 NULL 1708 Using where; Using temporary; Using filesort 

这意味着它必须手动查看1708条记录。指数等被使用，但1708仍然存在。这些记录将使用已知很慢的文件进行排序。

查询

LEFT OUTER JOIN field_data_field_item_workflow_status wsts ON wsts.entity_id = n.nid 

不基于表field_data_field_item_workflow_status一些选择。如果你可以在那里添加索引，我认为你必须关注。如果索引存在，也许它可以更好地描述？如果指数在那里，也许字段长度可以缩短？数据类型越大，索引越大。因此尽可能尝试使用TINYINT而不是INT。

无论如何你近在咫尺:)