SQL Script to alter ALL Foreign Keys to add ON DELETE CASCADE
Here's a script I used for a similiar purpose. It does not support composite foreign keys (which use more than one field.) And it would probably need some tweaking before it will work for your situation. EDIT: In particular it does not handle multi-column foreign keys correctly.
select
DropStmt = 'ALTER TABLE [' + ForeignKeys.ForeignTableSchema +
'].[' + ForeignKeys.ForeignTableName +
'] DROP CONSTRAINT [' + ForeignKeys.ForeignKeyName + ']; '
, CreateStmt = 'ALTER TABLE [' + ForeignKeys.ForeignTableSchema +
'].[' + ForeignKeys.ForeignTableName +
'] WITH CHECK ADD CONSTRAINT [' + ForeignKeys.ForeignKeyName +
'] FOREIGN KEY([' + ForeignKeys.ForeignTableColumn +
']) REFERENCES [' + schema_name(sys.objects.schema_id) + '].[' +
sys.objects.[name] + ']([' +
sys.columns.[name] + ']) ON DELETE CASCADE; '
from sys.objects
inner join sys.columns
on (sys.columns.[object_id] = sys.objects.[object_id])
inner join (
select sys.foreign_keys.[name] as ForeignKeyName
,schema_name(sys.objects.schema_id) as ForeignTableSchema
,sys.objects.[name] as ForeignTableName
,sys.columns.[name] as ForeignTableColumn
,sys.foreign_keys.referenced_object_id as referenced_object_id
,sys.foreign_key_columns.referenced_column_id as referenced_column_id
from sys.foreign_keys
inner join sys.foreign_key_columns
on (sys.foreign_key_columns.constraint_object_id
= sys.foreign_keys.[object_id])
inner join sys.objects
on (sys.objects.[object_id]
= sys.foreign_keys.parent_object_id)
inner join sys.columns
on (sys.columns.[object_id]
= sys.objects.[object_id])
and (sys.columns.column_id
= sys.foreign_key_columns.parent_column_id)
) ForeignKeys
on (ForeignKeys.referenced_object_id = sys.objects.[object_id])
and (ForeignKeys.referenced_column_id = sys.columns.column_id)
where (sys.objects.[type] = 'U')
and (sys.objects.[name] not in ('sysdiagrams'))
How to add 'ON DELETE CASCADE' in ALTER TABLE statement
You can not add ON DELETE CASCADE
to an already existing constraint. You will have to drop
and re-create
the constraint. The documentation shows that the MODIFY CONSTRAINT
clause can only modify the state of a constraint (i-e: ENABLED/DISABLED
...).
Remove ON DELETE CASCADE on foreign keys for several tables
I would not reinvent the wheel. There is excellent script written by Aaron Bertrand: Drop and Re-Create All Foreign Key Constraints in SQL Server.
You could easily extend it to handle NO ACTION
case and specific schema by adding simple WHERE
restriction:
DECLARE @drop NVARCHAR(MAX) = N'',
@create NVARCHAR(MAX) = N'';
-- drop is easy,just build a simple concatenated list from sys.foreign_keys:
SELECT @drop += N'
ALTER TABLE ' + QUOTENAME(cs.name) + '.' + QUOTENAME(ct.name)
+ ' DROP CONSTRAINT ' + QUOTENAME(fk.name) + ';'
FROM sys.foreign_keys AS fk
INNER JOIN sys.tables AS ct
ON fk.parent_object_id = ct.[object_id]
INNER JOIN sys.schemas AS cs
ON ct.[schema_id] = cs.[schema_id]
WHERE delete_referential_action_desc <> 'NO_ACTION' -- here
AND cs.name = 'datasets';
-- create is a little more complex. We need to generate the list of
-- columns on both sides of the constraint, even though in most cases
-- there is only one column.
SELECT @create += N'
ALTER TABLE '
+ QUOTENAME(cs.name) + '.' + QUOTENAME(ct.name)
+ ' ADD CONSTRAINT ' + QUOTENAME(fk.name)
+ ' FOREIGN KEY (' + STUFF((SELECT ',' + QUOTENAME(c.name)
-- get all the columns in the constraint table
FROM sys.columns AS c
INNER JOIN sys.foreign_key_columns AS fkc
ON fkc.parent_column_id = c.column_id
AND fkc.parent_object_id = c.[object_id]
WHERE fkc.constraint_object_id = fk.[object_id]
ORDER BY fkc.constraint_column_id
FOR XML PATH(N''), TYPE).value(N'.[1]', N'nvarchar(max)'),1,1,N'')
+ ') REFERENCES ' + QUOTENAME(rs.name) + '.' + QUOTENAME(rt.name)
+ '(' + STUFF((SELECT ',' + QUOTENAME(c.name)
-- get all the referenced columns
FROM sys.columns AS c
INNER JOIN sys.foreign_key_columns AS fkc
ON fkc.referenced_column_id = c.column_id
AND fkc.referenced_object_id = c.[object_id]
WHERE fkc.constraint_object_id = fk.[object_id]
ORDER BY fkc.constraint_column_id
FOR XML PATH(N''), TYPE).value(N'.[1]', N'nvarchar(max)'),1,1,N'') + ');'
FROM sys.foreign_keys AS fk
INNER JOIN sys.tables AS rt -- referenced table
ON fk.referenced_object_id = rt.[object_id]
INNER JOIN sys.schemas AS rs
ON rt.[schema_id] = rs.[schema_id]
INNER JOIN sys.tables AS ct -- constraint table
ON fk.parent_object_id = ct.[object_id]
INNER JOIN sys.schemas AS cs
ON ct.[schema_id] = cs.[schema_id]
WHERE rt.is_ms_shipped = 0 AND ct.is_ms_shipped = 0
AND delete_referential_action_desc <> 'NO_ACTION' -- here
AND cs.name = 'datasets';
print(@drop);
print(@create);
-- ...
DBFiddle Demo
One warning! Please avoid adding ORDER BY
.
This script uses
SELECT @drop += N'...'
<=>
SELECT @drop = @drop + N'...'
and it may start producing incorrect results. More nvarchar concatenation / index / nvarchar(max) inexplicable behavior
How to add on delete cascade constraints?
I'm pretty sure you can't simply add on delete cascade
to an existing foreign key constraint. You have to drop the constraint first, then add the correct version. In standard SQL, I believe the easiest way to do this is to
- start a transaction,
- drop the foreign key,
- add a foreign key with
on delete cascade
, and finally - commit the transaction
Repeat for each foreign key you want to change.
But PostgreSQL has a non-standard extension that lets you use multiple constraint clauses in a single SQL statement. For example
alter table public.scores
drop constraint scores_gid_fkey,
add constraint scores_gid_fkey
foreign key (gid)
references games(gid)
on delete cascade;
If you don't know the name of the foreign key constraint you want to drop, you can either look it up in pgAdminIII (just click the table name and look at the DDL, or expand the hierarchy until you see "Constraints"), or you can query the information schema.
select *
from information_schema.key_column_usage
where position_in_unique_constraint is not null
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