查看数据库中某张表的字段个数

Oracle中查询某个表的总字段数，要用SQL语句，或者在PL/SQL里面

select count(column_name) from user_tab_columns where table_name='T_B_AUDITOR'

能够查出来指定的那张表的字段数。

下面是通过大致查看：

select   tname,count(*)   from   col   group   by   tname;

64	T_A_BOOKSTAGEINFO	4
65	T_B_AUDITOR	14
66	T_B_BOOKMANAGEMENT	13
67	T_B_BOOKSTATUSCONFIG	5
68	T_B_CODETREEINFO	8
69	T_B_FILTERWORD	11
70	T_B_ISBNWHITELIST	11
71	T_B_MODEL	10
72	T_B_NOTICE	15
73	T_B_NOTICEACCEPT	11
74	T_B_OPERLOG	10
75	T_B_ORGANIZATIONINFO	18
76	T_B_PREFIXINFO	15
77	T_B_PUBLISHINFO	30
78	T_B_ROLE	8
79	T_B_ROLEMODEL	6
80	T_B_SAMPLEBOOKINFO	89
81	T_B_USER	26
82	T_B_USERANDROLE	6
83	T_B_USERLOGIN	8
84	T_B_USERMODEL	6

此时我就联想到了mysql上面去：

直接利用函数来解决：

mysql> desc test;
+---------+-------------+------+-----+---------+----------------+
| Field   | Type        | Null | Key | Default | Extra          |
+---------+-------------+------+-----+---------+----------------+
| id      | int(11)     | NO   | PRI | NULL    | auto_increment |
| name    | varchar(10) | YES  |     | NULL    |                |
| address | varchar(30) | YES  |     | NULL    |                |
+---------+-------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

mysql> select found_rows();
+--------------+
| found_rows() |
+--------------+
|            3 |
+--------------+
1 row in set (0.01 sec)

还有就是利用系统表：

mysql> use information_schema
Database changed
mysql> select count(*) from columns where table_name="test";
+----------+
| count(*) |
+----------+
|        3 |
+----------+
1 row in set (0.00 sec)

在mysql中想要知道数据库中有多少个库：

mysql> select * from schemata;
+--------------+--------------------+----------------------------+------------------------+----------+
| CATALOG_NAME | SCHEMA_NAME        | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH |
+--------------+--------------------+----------------------------+------------------------+----------+
| NULL         | information_schema | utf8                       | utf8_general_ci        | NULL     |
| NULL         | mysql              | utf8                       | utf8_general_ci        | NULL     |
| NULL         | test               | utf8                       | utf8_general_ci        | NULL     |
+--------------+--------------------+----------------------------+------------------------+----------+
3 rows in set (0.00 sec)

在mysql数据库中有多少张表：

mysql> select table_schema,count(*) from tables group by table_schema;
+--------------------+----------+
| table_schema       | count(*) |
+--------------------+----------+
| information_schema |       17 |
| mysql              |       17 |
| test               |        6 |
+--------------------+----------+
3 rows in set (0.00 sec)

其实在系统表information_schema中大多的数据库，表啊都会有记录的。所以要好好研究下这张表呢。