在Microsoft SQL Server中,我知道检查一个列是否存在默认约束并删除默认约束的查询是:

IF EXISTS(SELECT * FROM sysconstraints
  WHERE id=OBJECT_ID('SomeTable')
  AND COL_NAME(id,colid)='ColName'
  AND OBJECTPROPERTY(constid, 'IsDefaultCnst')=1)    
ALTER TABLE SomeTable DROP CONSTRAINT DF_SomeTable_ColName

但是由于以前版本的数据库的拼写错误,约束的名称可能是DF_SomeTable_ColName或DF_SmoeTable_ColName。

我如何删除默认约束没有任何SQL错误?默认的约束名称不会显示在INFORMATION_SCHEMA表中,这使得事情变得有点棘手。

因此,类似于'删除这个表/列中的默认约束',或'删除DF_SmoeTable_ColName',但如果它找不到它,不要给出任何错误。


当前回答

declare @ery nvarchar(max)
declare @tab nvarchar(max) = 'myTable'
declare @qu nvarchar(max) = 'alter table '+@tab+' drop constraint '

select @ery = (select bj.name from sys.tables as tb 
inner join sys.objects as bj 
on tb.object_id = bj.parent_object_id
where tb.name = @tab and bj.type = 'PK')

exec(@qu+@ery)

来看看。

其他回答

使用此命令浏览所有约束:

exec sp_helpconstraint 'mytable' --and look under constraint_name. 

它看起来像这样:DF__Mytable__Column__[ABC123]。然后你就可以去掉约束了。

declare @table_name nvarchar(100)
declare @col_name nvarchar(100)
declare @constraint nvarchar(100)
set @table_name = N'TableName'
set @col_name = N'ColumnName'

IF EXISTS (select       c.*
    from        sys.columns c 
    inner join  sys.tables t on t.object_id = c.object_id
    where       t.name = @table_name
    and         c.name = @col_name) 
BEGIN

select @constraint=d.name
from 
sys.tables t
join sys.default_constraints d on d.parent_object_id = t.object_id
join sys.columns c on c.object_id = t.object_id
and c.column_id = d.parent_column_id
where 
t.name = @table_name
and c.name = @col_name

    IF LEN(ISNULL(@constraint, '')) <> 0
    BEGIN
        DECLARE @sqlcmd VARCHAR(MAX)
        SET @sqlcmd = 'ALTER TABLE ' + QUOTENAME(@table_name) + ' DROP CONSTRAINT' + 
        QUOTENAME(@constraint);
        EXEC (@sqlcmd);

    END

END
GO

这将检查外键是否存在。如果它存在,那就放弃它。

DECLARE @SCHEMA_NAME NVARCHAR(256)
-- The table name you what drop the foreign key from.
DECLARE @ALTER_TABLE_NAME NVARCHAR(256)
-- The table name is liked with the foreign key.
DECLARE @REF_TABLE_NAME NVARCHAR(256) 
DECLARE @COMMAND  NVARCHAR(MAX)

SET @SCHEMA_NAME = N'MySchema';
SET @ALTER_TABLE_NAME = N'MyAlterTable';
SET @REF_TABLE_NAME = N'MyReferTable';

IF EXISTS (
    SELECT NAME
    FROM SYS.FOREIGN_KEYS
    WHERE PARENT_OBJECT_ID = (
        SELECT OBJECT_ID
        FROM SYS.OBJECTS
        WHERE OBJECT_ID = OBJECT_ID(@ALTER_TABLE_NAME)
    )
    AND REFERENCED_OBJECT_ID = (
        SELECT OBJECT_ID
        FROM SYS.OBJECTS
        WHERE OBJECT_ID = OBJECT_ID(@REF_TABLE_NAME)
    )
)
BEGIN
    SELECT @COMMAND = 'ALTER TABLE ['
        + @SCHEMA_NAME
        + '].['
        + @ALTER_TABLE_NAME
        + '] DROP CONSTRAINT '
        + NAME
    FROM SYS.FOREIGN_KEYS
    WHERE PARENT_OBJECT_ID = (
        SELECT OBJECT_ID
        FROM SYS.OBJECTS
        WHERE OBJECT_ID = OBJECT_ID(@ALTER_TABLE_NAME)
    )
    AND REFERENCED_OBJECT_ID = (
        SELECT OBJECT_ID
        FROM SYS.OBJECTS
        WHERE OBJECT_ID = OBJECT_ID(@REF_TABLE_NAME)
    )
    
    EXECUTE (@COMMAND)
END
GO

总是生成脚本并在运行之前进行检查。下面是脚本

  select 'Alter table dbo.' + t.name + ' drop constraint '+ d.name  
  from sys.tables t
  join sys.default_constraints d on d.parent_object_id = t.object_id
  join sys.columns c on c.object_id = t.object_id
       and c.column_id = d.parent_column_id
  where c.name in ('VersionEffectiveDate','VersionEndDate','VersionReasonDesc')
  order by t.name

适用于创建了多个默认约束或检查约束的列:

修改https://stackoverflow.com/a/16359095/206730脚本

注意:此脚本用于sys.check_constraints

declare @table_name nvarchar(128)
declare @column_name nvarchar(128)
declare @constraint_name nvarchar(128)
declare @constraint_definition nvarchar(512)

declare @df_name nvarchar(128)
declare @cmd nvarchar(128) 

PRINT 'DROP CONSTRAINT [Roles2016.UsersCRM].Estado'

declare constraints cursor for 
 select t.name TableName, c.name ColumnName, d.name ConstraintName, d.definition ConstraintDefinition
 from sys.tables t   
 join sys.check_constraints d  on d.parent_object_id = t.object_id  
 join sys.columns c  on c.object_id = t.object_id      
 and c.column_id = d.parent_column_id
 where t.name = N'Roles2016.UsersCRM' and c.name = N'Estado'

open constraints
fetch next from constraints into @table_name , @column_name, @constraint_name, @constraint_definition
while @@fetch_status = 0
BEGIN
    print 'CONSTRAINT: ' + @constraint_name
    select @cmd = 'ALTER TABLE [' + @table_name +  '] DROP CONSTRAINT [' +  @constraint_name + ']'
    print @cmd
    EXEC sp_executeSQL @cmd;

  fetch next from constraints into @table_name , @column_name, @constraint_name, @constraint_definition
END

close constraints 
deallocate constraints