Explain mysql query statement

Description of the return value of the explain SQL statement performance test: www.2cto.com SQL code mysql> Explain SELECT 'content _ id', 'content _ old_id ', 'content _ hasimg ', 'content _ time_update ', 'content _ title_long', 'vhost _ content '. 'site _ id', 'site _ domain ', 'site _ name ', 'site _ state' FROM 'vhost _ content' left join 'vhost _ site' ON 'vhost _ content '. 'site _ id' = 'vhost _ site '. 'site _ id' WHERE 'content _ effect '= 1 AND 'content _ audit' = 1 D 'content _ publish '= 1 AND 'content _ time_update'> = '2017-12-16 'AND 'vhost _ content '. 'site _ id' LIKE '200' AND 1 = 1 order by 'content _ time_update 'desc LIMIT 0, 25; + ---- + ------------- + --------------- + ------- + certificate + -------------------- + --------- + ----------------------------- + ------ + ----------------------------- + | id | sel Ect_type | table | type | possible_keys | key | key_len | ref | rows | Extra | + ---- + ------------- + ------- + certificate + ------------------ + --------- + keys + ------ + keys + | 1 | SIMPLE | vhost_content | range | idx_content_site, refvhost_site483, idx_content_uptime, idx_content _ Publish | idx_content_site | 55 | NULL | 198 | Using where; Using filesort | 1 | SIMPLE | vhost_site | ref | PRIMARY | 54 | vhostdb. vhost_content.site_id | 1 | + ---- + ------------- + --------------- + ------- + others + -------------------- + --------- + others + ------ + --------------------------- + www. 2ct O.com Table: displays the Type of the database Table involved in the statement. This column is very important and shows the category used by the connection, whether the index is used, and the statement quality. The result values are: system> const> eq_ref> ref> fulltext> ref_or_null> index_merge> unique_subquery> index_subquery> range> index> ALL. Generally, make sure that the query reaches the range level at least. It is best to reach the ref level; otherwise, performance problems may occur. Possible_key: indicates which index mysql can use to find the row Key in the table: displays the Key (INDEX) actually used by mysql. If no index is selected, the Key is null. Key_len: displays the key length determined by mysql. If it is null, the length is null. The shorter the length, the better, without compromising accuracy. Ref: displays the column or constant used with the key to select rows from the table. Rows: displays the number of Rows that mysql considers to be checked when performing a query. Extra: contains detailed information about mysql queries.