If you want to add a unique key constraint or index to a table that might have duplicate records you’re in for some fun. You can either delete the duplicates, or fix the data to make them unique.
Suppose you have a table “Widgets”, which should be unique on
SupplierId and Name, but isn’t. This tsql script will update the duplicates by appending a “(1)”, “(2)”, etc. to the Name, thus satisfying the proposed UKC:
DECLARE @Widgets TABLE( Id INT NOT NULL PRIMARY KEY, SupplierId INT NOT NULL, Name NVARCHAR(50) NOT NULL) INSERT INTO @Widgets (Id, SupplierId, Name) VALUES (1, 1, 'WidgetA'), (2, 2, 'WidgetA'), (3, 3, 'WidgetB'), (4, 3, 'WidgetB'), (5, 3, 'WidgetC'), (6, 3, 'WidgetC'), (7, 3, 'WidgetC') SELECT * FROM @Widgets ;WITH cte AS ( SELECT ROW_NUMBER() OVER(PARTITION BY SupplierId, Name ORDER BY Id) AS rno, Name FROM @Widgets ) UPDATE cte SET Name = Name + ' (' + CONVERT(varchar(10), rno) + ')' WHERE rno > 1 SELECT * FROM @Widgets
You ought to be able to run all that and get these results in SQL Server:
Adapt to your needs :).