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
Rob Farley的博客文章可能会有所帮助:
有两种方法可以在不知道默认约束名称的情况下查找/删除它
喜欢的东西:
declare @table_name nvarchar(256)
declare @col_name nvarchar(256)
set @table_name = N'Department'
set @col_name = N'ModifiedDate'
select t.name, c.name, d.name, d.definition
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
其他回答
Rob Farley的博客文章可能会有所帮助:
有两种方法可以在不知道默认约束名称的情况下查找/删除它
喜欢的东西:
declare @table_name nvarchar(256)
declare @col_name nvarchar(256)
set @table_name = N'Department'
set @col_name = N'ModifiedDate'
select t.name, c.name, d.name, d.definition
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
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)
我有一些列创建了多个默认约束，所以我创建了以下存储过程:
CREATE PROCEDURE [dbo].[RemoveDefaultConstraints] @table_name nvarchar(256), @column_name nvarchar(256)
AS
BEGIN
DECLARE @ObjectName NVARCHAR(100)
START: --Start of loop
SELECT
@ObjectName = OBJECT_NAME([default_object_id])
FROM
SYS.COLUMNS
WHERE
[object_id] = OBJECT_ID(@table_name)
AND [name] = @column_name;
-- Don't drop the constraint unless it exists
IF @ObjectName IS NOT NULL
BEGIN
EXEC ('ALTER TABLE '+@table_name+' DROP CONSTRAINT ' + @ObjectName)
GOTO START; --Used to loop in case of multiple default constraints
END
END
GO
-- How to run the stored proc. This removes the default constraint(s) for the enabled column on the User table.
EXEC [dbo].[RemoveDefaultConstraints] N'[dbo].[User]', N'enabled'
GO
-- If you hate the proc, just get rid of it
DROP PROCEDURE [dbo].[RemoveDefaultConstraints]
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
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)
