oracle数据库怎么查询某个表有多少个字段

1、创建测试表，

create table test_cols(id varchar2(20),remark varchar2(20),ex_filed1 varchar2(20),ex_filed2 varchar2(20))

2、编写sql，查看系统视图，可以看到该用户下所有表的字段信息，select * from user_tab_cols；

3、编写sql，查询刚创建的表，字段信息，select * from user_tab_cols t where table_name = 'TEST_COLS'

4、编写sql，查询该表的字段数，这样对于字段较多的表，结果更明显

 select count(distinct column_name) from user_tab_cols t where table_name = 'TEST_COLS'

1.查询数据库中的所有数据库名：

SELECT Name FROM Master..SysDatabases ORDER BY Name

2.查询某个数据库中所有的表名：

SELECT Name FROM SysObjects Where XType='U' ORDER BY Name

3.查询表结构信息：

1 SELECT (case when a.colorder=1 then d.name else null end) 表名,

2 a.colorder 字段序号,a.name 字段名,

3 (case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else '' end) 标识,

4 (case when (SELECT count(*) FROM sysobjects

5 WHERE (name in (SELECT name FROM sysindexes

6 WHERE (id = a.id) AND (indid in

7 (SELECT indid FROM sysindexkeys

8 WHERE (id = a.id) AND (colid in

9 (SELECT colid FROM syscolumns WHERE (id = a.id) AND (name = a.name)))))))

10 AND (xtype = 'PK'))>0 then '√' else '' end) 主键,b.name 类型,a.length 占用字节数,

11 COLUMNPROPERTY(a.id,a.name,'PRECISION') as 长度,

12 isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0) as 小数位数,(case when a.isnullable=1 then '√'else '' end) 允许空,

13 isnull(e.text,'') 默认值,isnull(g.[value], ' ') AS [说明]

14 FROM syscolumns a

15 left join systypes b on a.xtype=b.xusertype

16 inner join sysobjects d on a.id=d.id and d.xtype='U' and d.name<>'dtproperties'

17 left join syscomments e on a.cdefault=e.id

18 left join sys.extended_properties g on a.id=g.major_id AND a.colid=g.minor_id

19 left join sys.extended_properties f on d.id=f.class and f.minor_id=0

20 where b.name is not null

21 --WHERE d.name='要查询的表' --如果只查询指定表,加上此条件

22 order by a.id,a.colorder

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