Change auto-named SQL constraint

ChangeAutoNamedConstraint.sql

-- Table: Users
-- Column: Age
-- Constraint: auto-generated, e.g. DF__Users__Age__<random>

-- Find a specific constrait name assuming there is a single constraint only
DECLARE @ConstraintName nvarchar(100)
SELECT @ConstraintName = c.name FROM sys.default_constraints c 
INNER JOIN sys.columns col ON col.default_object_id = c.object_id 
WHERE c.parent_object_id = OBJECT_ID('dbo.Users') AND col.name = 'Age'

-- Drop the constraint if found
IF @ConstraintName IS NOT NULL 
BEGIN
	EXEC('ALTER TABLE [dbo].[Users] DROP CONSTRAINT ' + @ConstraintName)
END

-- Add a new constraint with a predefined name
ALTER TABLE [dbo].[Users] ADD DEFAULT ((0)) FOR [Age]

-- Blog post: https://ignas.me/tech/change-auto-named-sql-constraint/