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
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。
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
删除数据库安全的nvarchar(max)阈值中的所有默认约束。
/* WARNING: THE SAMPLE BELOW; DROPS ALL THE DEFAULT CONSTRAINTS IN A DATABASE */
/* MAY 03, 2013 - BY WISEROOT */
declare @table_name nvarchar(128)
declare @column_name nvarchar(128)
declare @df_name nvarchar(128)
declare @cmd nvarchar(128)
declare table_names cursor for
SELECT t.name TableName, c.name ColumnName
FROM sys.columns c INNER JOIN
sys.tables t ON c.object_id = t.object_id INNER JOIN
sys.schemas s ON t.schema_id = s.schema_id
ORDER BY T.name, c.name
open table_names
fetch next from table_names into @table_name , @column_name
while @@fetch_status = 0
BEGIN
if exists (SELECT top(1) 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 = @column_name)
BEGIN
SET @df_name = (SELECT top(1) 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 = @column_name)
select @cmd = 'ALTER TABLE [' + @table_name + '] DROP CONSTRAINT [' + @df_name + ']'
print @cmd
EXEC sp_executeSQL @cmd;
END
fetch next from table_names into @table_name , @column_name
END
close table_names
deallocate table_names
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)
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。
下面的解决方案将从表中删除列的特定默认约束
Declare @Const NVARCHAR(256)
SET @Const = (
SELECT TOP 1 'ALTER TABLE' + YOUR TABLE NAME +' DROP CONSTRAINT '+name
FROM Sys.default_constraints A
JOIN sysconstraints B on A.parent_object_id = B.id
WHERE id = OBJECT_ID('YOUR TABLE NAME')
AND COL_NAME(id, colid)='COLUMN NAME'
AND OBJECTPROPERTY(constid,'IsDefaultCnst')=1
)
EXEC (@Const)
