How can I find out what FOREIGN KEY constraint references a table in SQL Server?

I am trying to drop a table but getting the following message:

> Msg 3726, Level 16, State 1, Line 3
> Could not drop object 'dbo.UserProfile' because it is referenced by a FOREIGN KEY constraint.
> Msg 2714, Level 16, State 6, Line 2
> There is already an object named 'UserProfile' in the database.

I looked around with SQL Server Management Studio but I am unable to find the constraint. How can I find out the foreign key constraints?

if you want to go via SSMS on the object explorer window, right click on the object you want to drop, do view dependencies.

Try this


SELECT
object_name(parent_object_id) ParentTableName,
object_name(referenced_object_id) RefTableName,
name
FROM sys.foreign_keys
WHERE parent_object_id = object_id('Tablename')

Here it is:

SELECT
OBJECT_NAME(f.parent_object_id) TableName,
COL_NAME(fc.parent_object_id,fc.parent_column_id) ColName
FROM
sys.foreign_keys AS f
INNER JOIN
sys.foreign_key_columns AS fc
ON f.OBJECT_ID = fc.constraint_object_id
INNER JOIN
sys.tables t
ON t.OBJECT_ID = fc.referenced_object_id
WHERE
OBJECT_NAME (f.referenced_object_id) = 'YourTableName'

This way, you'll get the referencing table and column name.

Edited to use sys.tables instead of generic sys.objects as per comment suggestion.
Thanks, marc_s

try the following query.

select object_name(sfc.constraint_object_id) AS constraint_name,
OBJECT_Name(parent_object_id) AS table_name ,
ac1.name as table_column_name,
OBJECT_name(referenced_object_id) as reference_table_name,
ac2.name as reference_column_name
from sys.foreign_key_columns sfc
join sys.all_columns ac1 on (ac1.object_id=sfc.parent_object_id and ac1.column_id=sfc.parent_column_id)
join sys.all_columns ac2 on (ac2.object_id=sfc.referenced_object_id and ac2.column_id=sfc.referenced_column_id)
where sfc.parent_object_id=OBJECT_ID(<main table name>);

this will give the constraint_name, column_names which will be referring and tables which will be depending on the constraint will be there.

Here is the best way to find out Foreign Key Relationship in all Database.

exec sp_helpconstraint 'Table Name'

and one more way

select * from INFORMATION_SCHEMA.KEY_COLUMN_USAGE where TABLE_NAME='Table Name'
--and left(CONSTRAINT_NAME,2)='FK'(If you want single key)

I am using this script to find all details related to foreign key.
I am using INFORMATION.SCHEMA.
Below is a SQL Script:

SELECT
ccu.table_name AS SourceTable
,ccu.constraint_name AS SourceConstraint
,ccu.column_name AS SourceColumn
,kcu.table_name AS TargetTable
,kcu.column_name AS TargetColumn
FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE ccu
INNER JOIN INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS rc
ON ccu.CONSTRAINT_NAME = rc.CONSTRAINT_NAME
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu
ON kcu.CONSTRAINT_NAME = rc.UNIQUE_CONSTRAINT_NAME
ORDER BY ccu.table_name

--The following may give you more of what you're looking for:

create Procedure spShowRelationShips
(
@Table varchar(250) = null,
@RelatedTable varchar(250) = null
)
as
begin
if @Table is null and @RelatedTable is null
select object_name(k.constraint_object_id) ForeginKeyName,
object_name(k.Parent_Object_id) TableName,
object_name(k.referenced_object_id) RelatedTable,
c.Name RelatedColumnName,
object_name(rc.object_id) + '.' + rc.name RelatedKeyField
from sys.foreign_key_columns k
left join sys.columns c on object_name(c.object_id) = object_name(k.Parent_Object_id) and c.column_id = k.parent_column_id
left join sys.columns rc on object_name(rc.object_id) = object_name(k.referenced_object_id) and rc.column_id = k.referenced_column_id
order by 2,3

if @Table is not null and @RelatedTable is null
select object_name(k.constraint_object_id) ForeginKeyName,
object_name(k.Parent_Object_id) TableName,
object_name(k.referenced_object_id) RelatedTable,
c.Name RelatedColumnName,
object_name(rc.object_id) + '.' + rc.name RelatedKeyField
from sys.foreign_key_columns k
left join sys.columns c on object_name(c.object_id) = object_name(k.Parent_Object_id) and c.column_id = k.parent_column_id
left join sys.columns rc on object_name(rc.object_id) = object_name(k.referenced_object_id) and rc.column_id = k.referenced_column_id
where object_name(k.Parent_Object_id) =@Table
order by 2,3

if @Table is null and @RelatedTable is not null
select object_name(k.constraint_object_id) ForeginKeyName,
object_name(k.Parent_Object_id) TableName,
object_name(k.referenced_object_id) RelatedTable,
c.Name RelatedColumnName,
object_name(rc.object_id) + '.' + rc.name RelatedKeyField
from sys.foreign_key_columns k
left join sys.columns c on object_name(c.object_id) = object_name(k.Parent_Object_id) and c.column_id = k.parent_column_id
left join sys.columns rc on object_name(rc.object_id) = object_name(k.referenced_object_id) and rc.column_id = k.referenced_column_id
where object_name(k.referenced_object_id) =@RelatedTable
order by 2,3



end

You could use this query to display `Foreign key` constaraints:

SELECT
K_Table = FK.TABLE_NAME,
FK_Column = CU.COLUMN_NAME,
PK_Table = PK.TABLE_NAME,
PK_Column = PT.COLUMN_NAME,
Constraint_Name = C.CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C
INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS FK ON C.CONSTRAINT_NAME = FK.CONSTRAINT_NAME
INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS PK ON C.UNIQUE_CONSTRAINT_NAME = PK.CONSTRAINT_NAME
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE CU ON C.CONSTRAINT_NAME = CU.CONSTRAINT_NAME
INNER JOIN (
SELECT i1.TABLE_NAME, i2.COLUMN_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS i1
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE i2 ON i1.CONSTRAINT_NAME = i2.CONSTRAINT_NAME
WHERE i1.CONSTRAINT_TYPE = 'PRIMARY KEY'
) PT ON PT.TABLE_NAME = PK.TABLE_NAME
---- optional:
ORDER BY
1,2,3,4
WHERE PK.TABLE_NAME='YourTable'

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You can also return all the information about the `Foreign Keys` by adapating @LittleSweetSeas answer:

SELECT
OBJECT_NAME(f.parent_object_id) ConsTable,
OBJECT_NAME (f.referenced_object_id) refTable,
COL_NAME(fc.parent_object_id,fc.parent_column_id) ColName
FROM
sys.foreign_keys AS f
INNER JOIN
sys.foreign_key_columns AS fc
ON f.OBJECT_ID = fc.constraint_object_id
INNER JOIN
sys.tables t
ON t.OBJECT_ID = fc.referenced_object_id
order by
ConsTable