Shulou(Shulou.com)06/01 Report--

Optimize a mysql statement, there is no technical content, say the process:

The pre-optimization statement is as follows, which takes approximately 1-2 seconds to execute.

select u.id,u.s_user_name,u.s_user_img,(select count(a.n_copy_count) from t_fonts a join t_practicerecords b on b.n_font_id=a.id where a.n_user_id=u.id and b.n_delete=0 group by a.n_user_id)as n_copy_count, case when (select count(id) from t_friendships where n_user_id=11311 and n_friend_id=u.id)>0 then 'true' else 'false' end as is_collected from t_users u where BINARY ` s_user_name`='doing word-small helper ' order by LENGTH(s_user_name) asc ,id asc limit 0,10

The relevant implementation plans are as follows:

mysql> EXPLAIN select u.id ,u.s_user_name,u.s_user_img,(select count(a.n_copy_count) from t_fonts a join t_practicerecords b on b.n_font_id=a.id where a.n_user_id=u.id and b.n_delete=0 group by a.n_user_id)as n_copy_count,case when (select count(id) from t_friendships where n_user_id=11311 and n_friend_id=u.id)>0 then 'true' else 'false' end as is_collected from t_users u where BINARY `s_user_name` = 'Doing Word Little Assistant' order by LENGTH (s_user_name) asc ,id asc limit 0,10;+----+--------------------+---------------+------------+--------+-------------------------------------------------------------+---------------------------------+---------+------------------+---------+----------+-----------------------------+| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |+----+--------------------+---------------+------------+--------+-------------------------------------------------------------+---------------------------------+---------+------------------+---------+----------+-----------------------------+| 1 | PRIMARY | u | NULL | ALL | NULL | NULL | NULL | NULL | 1360606 | 100.00 | Using where; Using filesort || 3 | DEPENDENT SUBQUERY | t_friendships | NULL | eq_ref | PRIMARY,PK__T_friend__3213E83F571DF1D5,user_index,n_user_id | PRIMARY | 8 | const,sykdb.u.id | 1 | 100.00 | NULL || 2 | DEPENDENT SUBQUERY | a | NULL | ref | PRIMARY,n_user_index | n_user_index | 4 | sykdb.u.id | 7 | 100.00 | Using index condition || 2 | DEPENDENT SUBQUERY | b | NULL | ref | idx_fid_score_delete_uploadtime | idx_fid_score_delete_uploadtime | 5 | sykdb.a.id,const | 5 | 100.00 | Using index |+----+--------------------+---------------+------------+--------+-------------------------------------------------------------+---------------------------------+---------+------------------+---------+----------+-----------------------------+4 rows in set, 4 warnings (0.00 sec)

Create an index on the s_user_name field of the t_users table and modify the table structure

mysql> create index idx_user_name on t_users (s_user_name);Query OK, 0 rows affected (5.55 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> alter table t_users modify s_user_name varchar(100) binary;Query OK, 1474778 rows affected (45.23 sec)Records: 1474778 Duplicates: 0 Warnings: 0

Modify the statement to remove binary and query again as follows:

mysql> select u.id ,u.s_user_name,u.s_user_img,(select count(a.n_copy_count) from t_fonts a join t_practicerecords b on b.n_font_id=a.id where a.n_user_id=u.id and b.n_delete=0 group by a.n_user_id)as n_copy_count,case when (select count(id) from t_friendships where n_user_id=11311 and n_friend_id=u.id)>0 then 'true' else 'false' end as is_collected from t_users u where `s_user_name` = 'doing small helper' order by LENGTH(s_user_name) asc ,id asc limit 0,10;+--------------------------------| id | s_user_name | s_user_img | n_copy_count | is_collected |+----+-----------------+--------------------------------+--------------+--------------+| 2 |A little assistant.| /0/1/photo/20160729035328.jpeg | NULL | false |+----+-----------------+--------------------------------+--------------+--------------+1 row in set (0.00 sec)

However, caution should be exercised in modifying the table structure.

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