在SQLServer数据库中,如果查询数据库中是否存在指定名称的索引或者外键约束等,经常会用到object_id('name','type')方法,做笔记如下:
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语法:object_id('objectname')或object('objectname','type')
作用:该函数会返回指定对象的ID值,可以在sysobjects表中进行验证。
其中objectname数据类型为 char 或 nchar。如果 object 的数据类型是 char,那么隐性将其转换成 nchar。
type如下列表:
AF = Aggregate function (CLR)
C = CHECK constraint
D = DEFAULT (constraint or stand-alone)
F = FOREIGN KEY constraint
FN = SQL scalar function
FS = Assembly (CLR) scalar-function
FT = Assembly (CLR) table-valued function
IF = SQL inline table-valued function
IT = Internal table
P = SQL Stored Procedure
PC = Assembly (CLR) stored-procedure
PG = Plan guide
PK = PRIMARY KEY constraint
R = Rule (old-style, stand-alone)
RF = Replication-filter-procedure
S = System base table
SN = Synonym
SQ = Service queue
TA = Assembly (CLR) DML trigger
TF = SQL table-valued-function
TR = SQL DML trigger
U = Table (user-defined)
UQ = UNIQUE constraint
V = View
X = Extended stored procedure
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例子如下:
select object_id('fk_xxx_xx','F')会取出约束名为fk_xxx_xx的ID值,如返回144444444这个值。
上面的语句等同:
select ID from sysobjects where name='fk_xxx_xx' and type='F'
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大家都知道在数据库中有一个系统表sysobjects,里面存储了数据库各个对象的信息。可以查询下看看结果。可以看出每个对象都有一个ID,这个表存储了表,存储过程,触发器,视图等相关信息。注意:字段没有。
object_id就是根据对象名称返回该对象的id.
object_name是根据对象id返回对象名称.
select object_id(对象名)等同于:
select id from sysobjects where
name=对象名
select object_name(id号)等同于:
select name from sysobjects where id=id号
SQL SERVER
2000以上版本都支持这个函数。