问题
If I want to delete all the tables in my database like this, will it take care of the foreign key constraint? If not, how do I take care of that first?
GO
IF OBJECT_ID('dbo.[Course]','U') IS NOT NULL
DROP TABLE dbo.[Course]
GO
IF OBJECT_ID('dbo.[Student]','U') IS NOT NULL
DROP TABLE dbo.[Student]
回答1:
No, this will not drop your table if there are indeed foreign keys referencing it.
To get all foreign key relationships referencing your table, you could use this SQL (if you're on SQL Server 2005 and up):
SELECT *
FROM sys.foreign_keys
WHERE referenced_object_id = object_id('Student')
and if there are any, with this statement here, you could create SQL statements to actually drop those FK relations:
SELECT
'ALTER TABLE [' + OBJECT_SCHEMA_NAME(parent_object_id) +
'].[' + OBJECT_NAME(parent_object_id) +
'] DROP CONSTRAINT [' + name + ']'
FROM sys.foreign_keys
WHERE referenced_object_id = object_id('Student')
回答2:
In SQL Server Management Studio 2008 (R2) and newer, you can Right Click on the
DB -> Tasks -> Generate Scripts
Select the tables you want to DROP.
Select "Save to new query window".
Click on the Advanced button.
Set Script DROP and CREATE to Script DROP.
Set Script Foreign Keys to True.
Click OK.
Click Next -> Next -> Finish.
View the script and then Execute.
回答3:
If you drop the "child" table first, the foreign key will be dropped as well. If you attempt to drop the "parent" table first, you will get an "Could not drop object 'a' because it is referenced by a FOREIGN KEY constraint." error.
回答4:
Here is another way to drop all tables correctly, using sp_MSdropconstraints procedure. The shortest code I could think of:
exec sp_MSforeachtable "declare @name nvarchar(max); set @name = parsename('?', 1); exec sp_MSdropconstraints @name";
exec sp_MSforeachtable "drop table ?";
回答5:
If it is SQL Server you must drop the constraint before you can drop the table.
回答6:
Slightly more generic version of what @mark_s posted, this helped me
SELECT
'ALTER TABLE ' + OBJECT_SCHEMA_NAME(k.parent_object_id) +
'.[' + OBJECT_NAME(k.parent_object_id) +
'] DROP CONSTRAINT ' + k.name
FROM sys.foreign_keys k
WHERE referenced_object_id = object_id('your table')
just plug your table name, and execute the result of it.
回答7:
Here's another way to do delete all the constraints followed by the tables themselves, using a concatenation trick involving FOR XML PATH('') which allows merging multiple input rows into a single output row. Should work on anything SQL 2005 & later.
I've left the EXECUTE commands commented out for safety.
DECLARE @SQL NVARCHAR(max)
;WITH fkeys AS (
SELECT quotename(s.name) + '.' + quotename(o.name) tablename, quotename(fk.name) constraintname
FROM sys.foreign_keys fk
JOIN sys.objects o ON fk.parent_object_id = o.object_id
JOIN sys.schemas s ON o.schema_id = s.schema_id
)
SELECT @SQL = STUFF((SELECT '; ALTER TABLE ' + tablename + ' DROP CONSTRAINT ' + constraintname
FROM fkeys
FOR XML PATH('')),1,2,'')
-- EXECUTE(@sql)
SELECT @SQL = STUFF((SELECT '; DROP TABLE ' + quotename(TABLE_SCHEMA) + '.' + quotename(TABLE_NAME)
FROM INFORMATION_SCHEMA.TABLES
FOR XML PATH('')),1,2,'')
-- EXECUTE(@sql)
回答8:
Here is a complete script to implement a solution:
create Procedure [dev].DeleteTablesFromSchema
(
@schemaName varchar(500)
)
As
begin
declare @constraintSchemaName nvarchar(128), @constraintTableName nvarchar(128), @constraintName nvarchar(128)
declare @sql nvarchar(max)
-- delete FK first
declare cur1 cursor for
select distinct
CASE WHEN t2.[object_id] is NOT NULL THEN s2.name ELSE s.name END as SchemaName,
CASE WHEN t2.[object_id] is NOT NULL THEN t2.name ELSE t.name END as TableName,
CASE WHEN t2.[object_id] is NOT NULL THEN OBJECT_NAME(d2.constraint_object_id) ELSE OBJECT_NAME(d.constraint_object_id) END as ConstraintName
from sys.objects t
inner join sys.schemas s
on t.[schema_id] = s.[schema_id]
left join sys.foreign_key_columns d
on d.parent_object_id = t.[object_id]
left join sys.foreign_key_columns d2
on d2.referenced_object_id = t.[object_id]
inner join sys.objects t2
on d2.parent_object_id = t2.[object_id]
inner join sys.schemas s2
on t2.[schema_id] = s2.[schema_id]
WHERE t.[type]='U'
AND t2.[type]='U'
AND t.is_ms_shipped = 0
AND t2.is_ms_shipped = 0
AND s.Name=@schemaName
open cur1
fetch next from cur1 into @constraintSchemaName, @constraintTableName, @constraintName
while @@fetch_status = 0
BEGIN
set @sql ='ALTER TABLE ' + @constraintSchemaName + '.' + @constraintTableName+' DROP CONSTRAINT '+@constraintName+';'
exec(@sql)
fetch next from cur1 into @constraintSchemaName, @constraintTableName, @constraintName
END
close cur1
deallocate cur1
DECLARE @tableName nvarchar(128)
declare cur2 cursor for
select s.Name, p.Name
from sys.objects p
INNER JOIN sys.schemas s ON p.[schema_id] = s.[schema_id]
WHERE p.[type]='U' and is_ms_shipped = 0
AND s.Name=@schemaName
ORDER BY s.Name, p.Name
open cur2
fetch next from cur2 into @schemaName,@tableName
while @@fetch_status = 0
begin
set @sql ='DROP TABLE ' + @schemaName + '.' + @tableName
exec(@sql)
fetch next from cur2 into @schemaName,@tableName
end
close cur2
deallocate cur2
end
go
回答9:
Removing Referenced FOREIGN KEY Constraints
Assuming there is a parent and child table Relationship in SQL Server:
--First find the name of the Foreign Key Constraint:
SELECT *
FROM sys.foreign_keys
WHERE referenced_object_id = object_id('States')
--Then Find foreign keys referencing to dbo.Parent(States) table:
SELECT name AS 'Foreign Key Constraint Name',
OBJECT_SCHEMA_NAME(parent_object_id) + '.' + OBJECT_NAME(parent_object_id) AS 'Child Table'
FROM sys.foreign_keys
WHERE OBJECT_SCHEMA_NAME(referenced_object_id) = 'dbo' AND
OBJECT_NAME(referenced_object_id) = 'dbo.State'
-- Drop the foreign key constraint by its name
ALTER TABLE dbo.cities DROP CONSTRAINT FK__cities__state__6442E2C9;
-- You can also use the following T-SQL script to automatically find
--and drop all foreign key constraints referencing to the specified parent
-- table:
BEGIN
DECLARE @stmt VARCHAR(300);
-- Cursor to generate ALTER TABLE DROP CONSTRAINT statements
DECLARE cur CURSOR FOR
SELECT 'ALTER TABLE ' + OBJECT_SCHEMA_NAME(parent_object_id) + '.' +
OBJECT_NAME(parent_object_id) +
' DROP CONSTRAINT ' + name
FROM sys.foreign_keys
WHERE OBJECT_SCHEMA_NAME(referenced_object_id) = 'dbo' AND
OBJECT_NAME(referenced_object_id) = 'states';
OPEN cur;
FETCH cur INTO @stmt;
-- Drop each found foreign key constraint
WHILE @@FETCH_STATUS = 0
BEGIN
EXEC (@stmt);
FETCH cur INTO @stmt;
END
CLOSE cur;
DEALLOCATE cur;
END
GO
--Now you can drop the parent table:
DROP TABLE states;
--# Command(s) completed successfully.
回答10:
Using SQL Server Manager you can drop foreign key constraints from the UI. If you want to delete the table Diary but the User table has a foreign key DiaryId pointing to the Diary table, you can expand (using the plus symbol) the User table and then expand the Foreign Keys section. Right click on the foreign key that points to the diary table then select Delete. You can then expand the Columns section, right click and delete the column DiaryId too. Then you can just run:
drop table Diary
I know your actual question is about deleting all tables, so this may not be a useful for that case. However, if you just want to delete a few tables this is useful I believe (the title does not explicitly mention deleting all tables).
回答11:
If you are on a mysql server and if you don't mind loosing your tables, you can use a simple query to delete multiple tables at once:
SET foreign_key_checks = 0;
DROP TABLE IF EXISTS table_a,table_b,table_c,table_etc;
SET foreign_key_checks = 1;
In this way it doesn't matter in what order you use the table in you query.
If anybody is going to say something about the fact that this is not a good solution if you have a database with many tables: I agree!
回答12:
If I want to delete all the tables in my database
Then it's a lot easier to drop the entire database:
DROP DATABASE WorkerPensions
回答13:
If you want to DROP a table which has been referenced by other table using the foreign key use
DROP TABLE *table_name* CASCADE CONSTRAINTS;
I think it should work for you.
来源：https://stackoverflow.com/questions/1776079/sql-drop-table-foreign-key-constraint