如何改善我的选择查询？ 目前，以下选择查询大约需要2分钟才能执行。
SELECT COUNT( * ) AS count
FROM post
WHERE category REGEXP '[[:<:]](5|50|51|52|53|54|55|56|57|58|59|60|61|62|63|64|65|66|67|68|69|70|71|72|73|74|75|76|77|78|79|80|81|82|83|84|85|86|87|88|89|90|91|92|93|94|95|96|97|98|99|100|101|102|103|104|105|106|107|108|109|110|111|112|113|114|115|116|117|118|119|120|121|122|123|124|125|126|127|128|129|130|131|132|133|134|135|136|137|138|139|140|141|142|143|144|145|146|147|148|149|150|151|152|153|154|155|156|157|158|159|160|161|162|163|164|165|166|167|168|169|170|171|172|173|174|175|176|177|178|179|180|181|182|183|184|185|186|187|188|189|190|191|192|193|194|195|196|197|198|199|200|201|202|203|204|205|206|207|208|209|210|211|212|213|214|215|216|217|218|219|220|221|222|223|224|225|226|227|228|229|230|231|232|233|234|235|236|237)[[:>:]]'
AND approve =1
+-------+
| count |
+-------+
| 12718 |
+-------+
1 row in set (2 min 12.68 sec)
mysql> explain SELECT COUNT( * ) AS count FROM post WHERE category REGEXP '[[:<:]](5|50|51|52|53|54|55|56|57|58|59|60|61|62|63|64|65|66|67|68|69|70|71|72|73|74|75|76|77|78|79|80|81|82|83|84|85|86|87|88|89|90|91|92|93|94|95|96|97|98|99|100|101|102|103|104|105|106|107|108|109|110|111|112|113|114|115|116|117|118|119|120|121|122|123|124|125|126|127|128|129|130|131|132|133|134|135|136|137|138|139|140|141|142|143|144|145|146|147|148|149|150|151|152|153|154|155|156|157|158|159|160|161|162|163|164|165|166|167|168|169|170|171|172|173|174|175|176|177|178|179|180|181|182|183|184|185|186|187|188|189|190|191|192|193|194|195|196|197|198|199|200|201|202|203|204|205|206|207|208|209|210|211|212|213|214|215|216|217|218|219|220|221|222|223|224|225|226|227|228|229|230|231|232|233|234|235|236|237)[[:>:]]' AND approve =1;
+----+-------------+----------+------+---------------+---------+---------+-------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+------+---------------+---------+---------+-------+--------+-------------+
| 1 | SIMPLE | post | ref | approve | approve | 1 | const | 844258 | Using where |
+----+-------------+----------+------+---------------+---------+---------+-------+--------+-------------+
服务器版本：5.6.12-56 Percona Server（GPL），版本rc60.4，修订版393
启用了查询缓存。
mysql> show variables like "query%"
-> ;
+------------------------------+-----------+
| Variable_name | Value |
+------------------------------+-----------+
| query_alloc_block_size | 8192 |
| query_cache_limit | 10485760 |
| query_cache_min_res_unit | 4096 |
| query_cache_size | 536870912 |
| query_cache_strip_comments | OFF |
| query_cache_type | ON |
| query_cache_wlock_invalidate | OFF |
| query_prealloc_size | 8192 |
+------------------------------+-----------+
+-------------------------+-----------+
| Variable_name | Value |
+-------------------------+-----------+
| Qcache_free_blocks | 29707 |
| Qcache_free_memory | 297925216 |
| Qcache_hits | 2799738 |
| Qcache_inserts | 779490 |
| Qcache_lowmem_prunes | 0 |
| Qcache_not_cached | 256026 |
| Qcache_queries_in_cache | 110396 |
| Qcache_total_blocks | 253234 |
+-------------------------+-----------+