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

我发现这是有效的,没有使用连接:

DECLARE @ObjectName NVARCHAR(100)
SELECT @ObjectName = OBJECT_NAME([default_object_id]) FROM SYS.COLUMNS
WHERE [object_id] = OBJECT_ID('[tableSchema].[tableName]') AND [name] = 'columnName';
EXEC('ALTER TABLE [tableSchema].[tableName] DROP CONSTRAINT ' + @ObjectName)

只需确保columnName周围没有括号,因为查询正在寻找精确匹配,如果它是[columnName]则不会返回任何内容。

其他回答

删除多个列的约束:

declare @table_name nvarchar(256)

declare @Command nvarchar(max) = ''

set @table_name = N'ATableName'

select @Command = @Command + 'ALTER TABLE ' + @table_name + ' drop constraint ' + d.name + CHAR(10)+ CHAR(13)
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 in ('column1','column2','column3')

--print @Command

execute (@Command)

希望这能对有类似问题的人有所帮助。 在ObjectExplorer窗口中,选择您的数据库=> Tables,=> your table=> Constraints。如果客户是在创建列时定义的,则可以看到包含列名的缺省约束名。 然后使用:

ALTER TABLE  yourTableName DROP CONSTRAINT DF__YourTa__NewCo__47127295;

(约束名只是一个例子)

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。

扩展Mitch Wheat的代码,下面的脚本将生成删除约束并动态执行它的命令。

declare @schema_name nvarchar(256)
declare @table_name nvarchar(256)
declare @col_name nvarchar(256)
declare @Command  nvarchar(1000)

set @schema_name = N'MySchema'
set @table_name = N'Department'
set @col_name = N'ModifiedDate'

select @Command = 'ALTER TABLE ' + @schema_name + '.[' + @table_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 t.name = @table_name
  and t.schema_id = schema_id(@schema_name)
  and c.name = @col_name

--print @Command

execute (@Command)

扩展解决方案(考虑表模式):

-- Drop default contstraint for SchemaName.TableName.ColumnName
DECLARE @schema_name NVARCHAR(256)
DECLARE @table_name NVARCHAR(256)
DECLARE @col_name NVARCHAR(256)
DECLARE @Command  NVARCHAR(1000)

set @schema_name = N'SchemaName'
set @table_name = N'TableName'
set @col_name = N'ColumnName'

SELECT @Command = 'ALTER TABLE [' + @schema_name + '].[' + @table_name + '] DROP CONSTRAINT ' + d.name
 FROM sys.tables t   
  JOIN sys.default_constraints d       
   ON d.parent_object_id = t.object_id  
  JOIN sys.schemas s
        ON s.schema_id = t.schema_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 s.name = @schema_name 
  AND c.name = @col_name

EXECUTE (@Command)