[sql] Drop default constraint on a column in TSQL

I have a table with a column like this that is currently live:

name NVARCHAR(128) NOT NULL DEFAULT ''

I am altering the column like this to make it nullable:

ALTER TABLE  mytable ALTER COLUMN name NVARCHAR(128) NULL

However, the default constraint, named 'DF__mytable__datab__7DE4B36' in one instance of the table, still remains. I know this could have been avoided if the original author named the constraint. I have several of instances of these tables but I don't want to manually delete every constraint in every table I have. What is the easiest and most elegant way of dropping this default constraint on a column in Sql Server that I can uniformily apply to every instance of this table?

EDIT

This is the script that I ended up using:

DECLARE @table_id AS INT
DECLARE @name_column_id AS INT
DECLARE @sql nvarchar(255) 

-- Find table id
SET @table_id = OBJECT_ID('mytable')

-- Find name column id
SELECT @name_column_id = column_id
FROM sys.columns
WHERE object_id = @table_id
AND name = 'name'

-- Remove default constraint from name column
SELECT @sql = 'ALTER TABLE mytable DROP CONSTRAINT ' + D.name
FROM sys.default_constraints AS D
WHERE D.parent_object_id = @table_id
AND D.parent_column_id = @name_column_id
EXECUTE sp_executesql @sql

Another script that can be used to accomplish this can be found here: How to drop SQL default constraint without knowing its name?

Thanks!

I would suggest:

DECLARE @sqlStatement nvarchar(MAX),
        @tableName nvarchar(50) = 'TripEvent',
        @columnName nvarchar(50) = 'CreatedDate';

SELECT                  @sqlStatement = 'ALTER TABLE ' + @tableName + ' DROP CONSTRAINT ' + dc.name + ';'
        FROM            sys.default_constraints AS dc
            LEFT JOIN   sys.columns AS sc
                ON      (dc.parent_column_id = sc.column_id)
        WHERE           dc.parent_object_id = OBJECT_ID(@tableName)
        AND         type_desc = 'DEFAULT_CONSTRAINT'
        AND         sc.name = @columnName
PRINT'   ['+@tableName+']:'+@@SERVERNAME+'.'+DB_NAME()+'@'+CONVERT(VarChar, GETDATE(), 127)+';  '+@sqlStatement;
IF(LEN(@sqlStatement)>0)EXEC sp_executesql @sqlStatement

I would like to refer a previous question, Because I have faced same problem and solved by this solution. First of all a constraint is always built with a Hash value in it's name. So problem is this HASH is varies in different Machine or Database. For example DF__Companies__IsGlo__6AB17FE4 here 6AB17FE4 is the hash value(8 bit). So I am referring a single script which will be fruitful to all

DECLARE @Command NVARCHAR(MAX)
     declare @table_name nvarchar(256)
     declare @col_name nvarchar(256)
     set @table_name = N'ProcedureAlerts'
     set @col_name = N'EmailSent'

     select @Command ='Alter Table dbo.ProcedureAlerts Drop Constraint [' + ( select 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) + ']'

    --print @Command
    exec sp_executesql @Command

It will drop your default constraint. However if you want to create it again you can simply try this

ALTER TABLE [dbo].[ProcedureAlerts] ADD DEFAULT((0)) FOR [EmailSent]

Finally, just simply run a DROP command to drop the column.