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mysql> explain SELECT * from uchome_feed force index(uid) WHERE uid IN ('0',16,109,164,182,238,268,388,403,475);
+----+-------------+-------------+------+---------------+------+---------+------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+------+---------------+------+---------+------+--------+-------------+
| 1 | SIMPLE | uchome_feed | ALL | uid | NULL | NULL | NULL | 449779 | Using where |
+----+-------------+-------------+------+---------------+------+---------+------+--------+-------------+

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mysql> show index from uchome_feed;
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| uchome_feed | 0 | PRIMARY | 1 | feedid | A | 449779 | NULL | NULL | | BTREE | |
| uchome_feed | 1 | uid | 1 | uid | A | 449779 |