我有一个表,其中一列是datetime类型的“日期”。我们决定给该列添加一个默认约束
Alter table TableName
alter column dbo.TableName.Date default getutcdate()
但是这会让我出现错误:
附近有“.”的语法不正确。
除了列名应该取一个更好的名称之外,有人看到这里明显有什么问题吗,而我却没有察觉到?
我有一个表,其中一列是datetime类型的“日期”。我们决定给该列添加一个默认约束
Alter table TableName
alter column dbo.TableName.Date default getutcdate()
但是这会让我出现错误:
附近有“.”的语法不正确。
除了列名应该取一个更好的名称之外,有人看到这里明显有什么问题吗,而我却没有察觉到?
试试这个。
alter table TableName
add constraint df_ConstraintNAme
default getutcdate() for [Date]
例子
create table bla (id int)
alter table bla add constraint dt_bla default 1 for id
insert bla default values
select * from bla
还要确保给默认约束命名...因为它将拥有那些疯狂的系统生成名称,稍后删除它将会很麻烦...也请参阅如何命名默认约束以及如何在SQL Server中删除没有名称的默认约束
您可以将保留字用方括号括起来,以避免此类错误:
dbo.TableName.[Date]
drop table ABC_table
create table ABC_table
(
names varchar(20),
age int
)
ALTER TABLE ABC_table
ADD CONSTRAINT MyConstraintName
DEFAULT 'This is not NULL' FOR names
insert into ABC(age) values(10)
select * from ABC
我使用下面的存储过程来更新列上的默认值。
它会自动删除该列上的先前默认值,然后添加新的默认值。
用法示例:
-- Update default to be a date.
exec [dbo].[AlterDefaultForColumn] '[dbo].[TableName]','Column','getdate()';
-- Update default to be a number.
exec [dbo].[AlterDefaultForColumn] '[dbo].[TableName]','Column,'6';
-- Update default to be a string. Note extra quotes, as this is not a function.
exec [dbo].[AlterDefaultForColumn] '[dbo].[TableName]','Column','''MyString''';
存储过程:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- Sample function calls:
--exec [dbo].[AlterDefaultForColumn] '[dbo].[TableName]','ColumnName','getdate()';
--exec [dbol].[AlterDefaultForColumn] '[dbo].[TableName]','Column,'6';
--exec [dbo].[AlterDefaultForColumn] '[dbo].[TableName]','Column','''MyString''';
create PROCEDURE [dbo].[ColumnDefaultUpdate]
(
-- Table name, including schema, e.g. '[dbo].[TableName]'
@TABLE_NAME VARCHAR(100),
-- Column name, e.g. 'ColumnName'.
@COLUMN_NAME VARCHAR(100),
-- New default, e.g. '''MyDefault''' or 'getdate()'
-- Note that if you want to set it to a string constant, the contents
-- must be surrounded by extra quotes, e.g. '''MyConstant''' not 'MyConstant'
@NEW_DEFAULT VARCHAR(100)
)
AS
BEGIN
-- Trim angle brackets so things work even if they are included.
set @COLUMN_NAME = REPLACE(@COLUMN_NAME, '[', '')
set @COLUMN_NAME = REPLACE(@COLUMN_NAME, ']', '')
print 'Table name: ' + @TABLE_NAME;
print 'Column name: ' + @COLUMN_NAME;
DECLARE @ObjectName NVARCHAR(100)
SELECT @ObjectName = OBJECT_NAME([default_object_id]) FROM SYS.COLUMNS
WHERE [object_id] = OBJECT_ID(@TABLE_NAME) AND [name] = @COLUMN_NAME;
IF @ObjectName <> ''
begin
print 'Removed default: ' + @ObjectName;
--print('ALTER TABLE ' + @TABLE_NAME + ' DROP CONSTRAINT ' + @ObjectName)
EXEC('ALTER TABLE ' + @TABLE_NAME + ' DROP CONSTRAINT ' + @ObjectName)
end
EXEC('ALTER TABLE ' + @TABLE_NAME + ' ADD DEFAULT (' + @NEW_DEFAULT + ') FOR ' + @COLUMN_NAME)
--print('ALTER TABLE ' + @TABLE_NAME + ' ADD DEFAULT (' + @NEW_DEFAULT + ') FOR ' + @COLUMN_NAME)
print 'Added default of: ' + @NEW_DEFAULT;
END
该存储过程能够消除以下错误
如果您尝试为已经存在默认值的列添加一个默认值,将会出现以下错误(如果使用此存储过程,您将永远不会看到这个错误):
-- Using the stored procedure eliminates this error:
Msg 1781, Level 16, State 1, Line 1
Column already has a DEFAULT bound to it.
Msg 1750, Level 16, State 0, Line 1
Could not create constraint. See previous errors.
ALTER TABLE [TableName]
ADD DEFAULT (getutcdate()) FOR [Date];
修改表 TableName 删除约束 DF_TableName_WhenEntered
修改表 TableName 添加约束 DF_TableName_WhenEntered 默认值为 getutcdate(),用于 WhenEntered
您正在指定表名两次。 ALTER TABLE 部分命名了表格。 尝试: Alter table TableName alter column [Date] default getutcdate()