How to drop SQL default constraint without knowing its name? - sql

Question

In Microsoft SQL Server, I know the query to check if a default constraint exists for a column and drop a default constraint is:
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
But due to typo in previous versions of the database, the name of the constraint could be DF_SomeTable_ColName or DF_SmoeTable_ColName.
How can I delete the default constraint without any SQL errors? Default constraint names don't show up in INFORMATION_SCHEMA table, which makes things a bit trickier.
So, something like 'delete the default constraint in this table/column', or 'delete DF_SmoeTable_ColName', but don't give any errors if it can't find it.

Answer 1

Expanding on Mitch Wheat's code, the following script will generate the command to drop the constraint and dynamically execute it.
declare #schema_name nvarchar(256)
declare #table_name nvarchar(256)
declare #col_name nvarchar(256)
declare #Command nvarchar(1000)
set #schema_name = N'MySchema'
set #table_name = N'Department'
set #col_name = N'ModifiedDate'
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.columns c on c.object_id = t.object_id and c.column_id = d.parent_column_id
where t.name = #table_name
and t.schema_id = schema_id(#schema_name)
and c.name = #col_name
--print #Command
execute (#Command)

Answer 2

Rob Farley's blog post might be of help:
Two ways to find / drop a default constraint without knowing its name
Something like:
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

Answer 3

I found that this works and uses no joins:
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)
Just make sure that columnName does not have brackets around it because the query is looking for an exact match and will return nothing if it is [columnName].

Answer 4

To drop constraint for multiple columns:
declare #table_name nvarchar(256)
declare #Command nvarchar(max) = ''
set #table_name = N'ATableName'
select #Command = #Command + 'ALTER TABLE ' + #table_name + ' drop constraint ' + d.name + CHAR(10)+ CHAR(13)
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 in ('column1','column2','column3')
--print #Command
execute (#Command)

Answer 5

Expanded solution (takes table schema into account):
-- 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)

Answer 6

Run this command to browse all constraints:
exec sp_helpconstraint 'mytable' --and look under constraint_name.
It will look something like this: DF__Mytable__Column__[ABC123]. Then you can just drop the constraint.

Answer 7

Drop all default contstraints in a database - safe for nvarchar(max) threshold.
/* 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

Answer 8

I hope this could be helpful for whom has similar problem .
In ObjectExplorer window, select your database=> Tables,=> your table=> Constraints. If the customer is defined on create column time, you can see the default name of constraint including the column name.
then use:
ALTER TABLE yourTableName DROP CONSTRAINT DF__YourTa__NewCo__47127295;
(the constraint name is just an example)

Answer 9

Following solution will drop specific default constraint of a column from the table
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)

Answer 10

declare #ery nvarchar(max)
declare #tab nvarchar(max) = 'myTable'
declare #qu nvarchar(max) = 'alter table '+#tab+' drop constraint '
select #ery = (select bj.name from sys.tables as tb
inner join sys.objects as bj
on tb.object_id = bj.parent_object_id
where tb.name = #tab and bj.type = 'PK')
exec(#qu+#ery)
Take a look.

Answer 11

I had some columns that had multiple default constraints created, so I create the following stored procedure:
CREATE PROCEDURE [dbo].[RemoveDefaultConstraints] #table_name nvarchar(256), #column_name nvarchar(256)
AS
BEGIN
DECLARE #ObjectName NVARCHAR(100)
START: --Start of loop
SELECT
#ObjectName = OBJECT_NAME([default_object_id])
FROM
SYS.COLUMNS
WHERE
[object_id] = OBJECT_ID(#table_name)
AND [name] = #column_name;
-- Don't drop the constraint unless it exists
IF #ObjectName IS NOT NULL
BEGIN
EXEC ('ALTER TABLE '+#table_name+' DROP CONSTRAINT ' + #ObjectName)
GOTO START; --Used to loop in case of multiple default constraints
END
END
GO
-- How to run the stored proc. This removes the default constraint(s) for the enabled column on the User table.
EXEC [dbo].[RemoveDefaultConstraints] N'[dbo].[User]', N'enabled'
GO
-- If you hate the proc, just get rid of it
DROP PROCEDURE [dbo].[RemoveDefaultConstraints]
GO

Answer 12

Useful for some columns that had multiple default constraints or check constraints created:
Modified https://stackoverflow.com/a/16359095/206730 script
Note: this script is for 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

Answer 13

Always generate script and review before you run. Below the script
select 'Alter table dbo.' + t.name + ' drop constraint '+ 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 c.name in ('VersionEffectiveDate','VersionEndDate','VersionReasonDesc')
order by t.name

Answer 14

declare #table_name nvarchar(100)
declare #col_name nvarchar(100)
declare #constraint nvarchar(100)
set #table_name = N'TableName'
set #col_name = N'ColumnName'
IF EXISTS (select c.*
from sys.columns c
inner join sys.tables t on t.object_id = c.object_id
where t.name = #table_name
and c.name = #col_name)
BEGIN
select #constraint=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 = #col_name
IF LEN(ISNULL(#constraint, '')) <> 0
BEGIN
DECLARE #sqlcmd VARCHAR(MAX)
SET #sqlcmd = 'ALTER TABLE ' + QUOTENAME(#table_name) + ' DROP CONSTRAINT' +
QUOTENAME(#constraint);
EXEC (#sqlcmd);
END
END
GO

Answer 15

This will check if the foreign key exists or not. If it exists, then drop that.
DECLARE #SCHEMA_NAME NVARCHAR(256)
-- The table name you what drop the foreign key from.
DECLARE #ALTER_TABLE_NAME NVARCHAR(256)
-- The table name is liked with the foreign key.
DECLARE #REF_TABLE_NAME NVARCHAR(256)
DECLARE #COMMAND NVARCHAR(MAX)
SET #SCHEMA_NAME = N'MySchema';
SET #ALTER_TABLE_NAME = N'MyAlterTable';
SET #REF_TABLE_NAME = N'MyReferTable';
IF EXISTS (
SELECT NAME
FROM SYS.FOREIGN_KEYS
WHERE PARENT_OBJECT_ID = (
SELECT OBJECT_ID
FROM SYS.OBJECTS
WHERE OBJECT_ID = OBJECT_ID(#ALTER_TABLE_NAME)
)
AND REFERENCED_OBJECT_ID = (
SELECT OBJECT_ID
FROM SYS.OBJECTS
WHERE OBJECT_ID = OBJECT_ID(#REF_TABLE_NAME)
)
)
BEGIN
SELECT #COMMAND = 'ALTER TABLE ['
+ #SCHEMA_NAME
+ '].['
+ #ALTER_TABLE_NAME
+ '] DROP CONSTRAINT '
+ NAME
FROM SYS.FOREIGN_KEYS
WHERE PARENT_OBJECT_ID = (
SELECT OBJECT_ID
FROM SYS.OBJECTS
WHERE OBJECT_ID = OBJECT_ID(#ALTER_TABLE_NAME)
)
AND REFERENCED_OBJECT_ID = (
SELECT OBJECT_ID
FROM SYS.OBJECTS
WHERE OBJECT_ID = OBJECT_ID(#REF_TABLE_NAME)
)
EXECUTE (#COMMAND)
END
GO

Answer 16

Here is a simple solution, just replace your_table and the 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