SELECT posts.* FROM posts force index (idx_post_date) INNER JOIN follow ON follow.followuserid = posts.userid WHERE follow.userid=’61585′ ORDER BY date DESC LIMIT 0, 20;

The table posts has ~1000000 records and the number of records in the posts table belonging to userid 61585 is 0.

The table follow has 63537 records.

This is how my indexes are set:-

mysql> show index from follow;
+——–+————+———-+————–+————–+———–+————-+———-+——–+——+————+———+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+——–+————+———-+————–+————–+———–+————-+———-+——–+——+————+———+
| follow | 0 | PRIMARY | 1 | userid | A | NULL | NULL | NULL | | BTREE | |
| follow | 0 | PRIMARY | 2 | followuserid | A | 63537 | NULL | NULL | | BTREE | |
+——–+————+———-+————–+————–+———–+————-+———-+——–+——+————+———+

mysql> show index from posts;
+——-+————+——————+————–+————-+———–+————-+———-+——–+——+————+———+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+——-+————+——————+————–+————-+———–+————-+———-+——–+——+————+———+
| posts | 0 | PRIMARY | 1 | id | A | 1047467 | NULL | NULL | | BTREE | |
| posts | 1 | idx_post_date | 1 | date | A | 1047467 | NULL | NULL | | BTREE | |
| posts | 1 | idx_posts_userid | 1 | userid | A | 22771 | NULL | NULL | | BTREE | |
+——-+————+——————+————–+————-+———–+————-+———-+——–+——+————+———+

mysql> explain SELECT posts.* FROM posts force index (idx_post_date) INNER JOIN follow ON follow.followuserid = posts.userid WHERE follow.userid=’61585′ ORDER BY date DESC LIMIT 0, 20;
+—-+————-+——–+——–+—————+—————+———+——————————-+——+————-+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+—-+————-+——–+——–+—————+—————+———+——————————-+——+————-+
| 1 | SIMPLE | posts | index | NULL | idx_post_date | 4 | NULL | 20 | |
| 1 | SIMPLE | follow | eq_ref | PRIMARY | PRIMARY | 8 | const,wwwproject.posts.userid | 1 | Using index |
+—-+————-+——–+——–+—————+—————+———+——————————-+——+————-+

Is there a way to optimize this query i have now been trying for quite some time but could not find a solution any help would be very much appreciated??

MySQL can only use one index in a query (basically), so you need an index that contains all the columns you are filtering and ordering by, in the same order.

I would like to know ways to optimize the query above. SO retrieve last 100 records from TAble A matching the criteria in where clause

select ID_MEMBER_STARTED, COUNT(*) as hits from smf_topics group by ID_MEMBER_STARTED order by hits desc limit 20;

There is an index on ID_MEMBER_STARTED and the table type is InnoDB.