A few posts ago I published a Script to generate Trigger definitions. This week’s topic covers another automation script to generate scripts, this time related to DEFAULT Constraints. Simplistically put, whenever a DEFAULT constraint is definied on a table column, if the column is set to disallow NULL values and no value is defined for that column when the row is created, the default value (or derived default value) is used instead. Creating a DEFAULT constraint is achieved using the following syntax:
ALTER TABLE [ database_name . [ schema_name ] . | schema_name . ] table_name ADD CONSTRAINT constraint_name DEFAULT constraint_definition FOR column_name;
Once the constraints have been created, the defintions can be reviewed using the sys.default_constraints (Transact-SQL) DMV. In the below script I used this DMS as well as others (see below) to generate the DEFAULT constraint definitions for a database migration.
SET NOCOUNT ON; SELECT 'USE ' + QUOTENAME(DB_NAME(), '[') + ' GO'; SELECT 'ALTER TABLE ' + QUOTENAME(s.[name], '[') + '.' + QUOTENAME(tb.[name], '[') + ' ADD CONSTRAINT ' + QUOTENAME(df.[name], '[') + ' DEFAULT ' + df.[definition] + ' FOR ' + QUOTENAME(c.[name], '[') + ' GO ' FROM sys.default_constraints df INNER JOIN sys.tables tb ON df.[parent_object_id] = tb.[object_id] INNER JOIN sys.schemas s ON df.[schema_id] = s.[schema_id] INNER JOIN sys.columns c ON df.[parent_column_id] = c.[column_id] AND tb.[object_id] = c.[object_id] ORDER BY s.[name], tb.[name], df.[name];
The output could then be stored for documentation purposes or say, extracted from a development environment and relased on a test or production one. Whatever your choice, I am quite sure this will shave a few minutes off your database migration projects.