在实际的开发中，我们肯定经常要查看表结构的，特别是遇到自己不是最初开发的项目的时候，通过表结构，大概就能看出表里存什么数据，每个字段代表什么意思。实际上有很多查看表结构的方式，下面就拿rails里面的表schema_migrations介绍一下我自己常用的命令：
desc table_name;
mysql> desc schema_migrations;
+---------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+-------+
| version | varchar(255) | NO | PRI | NULL | |
+---------+--------------+------+-----+---------+-------+
1 row in set (0.00 sec)
它是我们最常用的命令，这个命令也是describe schema_migrations的缩写。
show fields from table_name;
mysql> show fields from schema_migrations;
+---------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+-------+
| version | varchar(255) | NO | PRI | NULL | |
+---------+--------------+------+-----+---------+-------+
1 row in set (0.01 sec)
和describe命令达到的效果一样。
在它的基础上就有一个更强大的命令：
show full fields from table_name
mysql> show full fields from schema_migrations;
+---------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment |
+---------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| version | varchar(255) | utf8_general_ci | NO | PRI | NULL | | select,insert,update,references | |
+---------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
1 row in set (0.01 sec)
每个字段的详细信息也就出来了，但是遗憾的是索引没有处理，说到查看索引，很明显就会想到下面的命令：
show index from table_name
mysql> show index from schema_migrations;
+-------------------+------------+--------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------------+------------+--------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| schema_migrations | 0 | unique_schema_migrations | 1 | version | A | 21 | NULL | NULL | | BTREE | | |
+-------------------+------------+--------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)
这个命令和show keys from table_name得到的效果一样。
实际上有个终极命令，既可以看到本身的字段又可以看到索引等其他信息，还能得到完整的创建表结构的命令，那就是：
show create table table_name
mysql> show create table schema_migrations;
+-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| schema_migrations | CREATE TABLE `schema_migrations` (
`version` varchar(255) NOT NULL,
UNIQUE KEY `unique_schema_migrations` (`version`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
通过命令执行的结果可以看到创建表的sql语句，字段名，索引，搜索引擎，编码方式等信息，是不是很强大。