从Mysql EXPLAIN探寻数据库查询优化(二)
nt |
| parent_id | int(11) | NO | | 0 | |
| title | varchar(255) | NO | | | |
| name | varchar(255) | NO | | | |
| alias | varchar(255) | NO | | | |
| image | varchar(255) | NO | | | |
| section | varchar(50) | NO | | | |
| image_position | varchar(30) | NO | | | |
| description | text | NO | | NULL | |
| published | tinyint(1) | NO | | 0 | |
| checked_out | int(11) unsigned | NO | | 0 | |
| checked_out_time | datetime | NO | | 0000-00-00 00:00:00 | |
| editor | varchar(50) | YES | | NULL | |
| ordering | int(11) | NO | | 0 | |
| access | tinyint(3) unsigned | NO | | 0 | |
| count | int(11) | NO | | 0 | |
| params | text | NO | | NULL | |
+------------------+---------------------+------+-----+---------------------+----------------+
17 rows in set (0.00 sec)
mysql> select count(*) from jos_categories;
+----------+
| count(*) |
+----------+
| 18 |
+----------+
1 row in set (0.00 sec)
mysql> desc jos_sections;
+------------------+---------------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------------+---------------------+------+-----+---------------------+----------------+ www.2cto.com
| title | varchar(255) | NO | | | |
| name | varchar(255) | NO | | | |
| alias | varchar(255) | NO | | | |
| image | text | NO | | NULL | |
| scope | varchar(50) | NO | | | |
| image_position | varchar(30) | NO | | | |
| description | text | NO | | NULL | |
| published | tinyint(1) | NO | | 0 | |
| checked_out | int(11) unsigned | NO | | 0 | |
| checked_out_time | datetime | NO | | 0000-00-00 00:00:00 | |
| ordering | int(11) | NO | | 0 | |
| access | tinyint(3) unsigned | NO | | 0 | |
| count | int(11) | NO | | 0 | |
| params | text | NO | | NULL | |
+------------------+---------------------+------+-----+---------------------+----------------+
15 rows in set (0.00 sec)
mysql> select count(*) from jos_sections;
+----------+
| count(*) |
+----------+
| 2 |
+----------+
1 row in set (0.00 sec)
简单说明：
jos_sections我们可以称它为大类表，jos_categories为小类表，jos_content为文章表，三个表的记录数分别为2、18、46585。
重要的字段基本上可以见名知义，只对几个联结字段说明一下：
jos_categories.secion: 这个字段是jos_section的主键id，它表明了大类和小类的父子关系，至于jos_categories.parent_id，我们可以先无视它的存在。
jos_content.sectionid: 这个字段也是jos_section的主键id，它表明了文章所属的大类。
jos_c