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
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
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
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。
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)
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)
这里有一个简单的解决方案，只需替换your_table和column_name。
DECLARE @var0 nvarchar(128)
SELECT @var0 = name
FROM sys.default_constraints
WHERE parent_object_id = object_id(N'${default_schema}.your_table')
AND col_name(parent_object_id, parent_column_id) = 'column_name';
IF @var0 IS NOT NULL
EXECUTE ('ALTER TABLE ${default_schema}.your_table DROP CONSTRAINT [' + @var0 + ']');
GO
