优化一个mysql语句
mysql> EXPLAIN selectu.id ,u.s_user_name,u.s_user_img,(select count(a.n_copy_count) from t_fonts ajoin 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_collectedfrom t_users u where BINARY `s_user_name` = '做字小助手'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)
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