Getting away from Dedupe jobs

Duplicate data should ideally be stopped at the front end. However if a table already contains duplicate data you may want to bash out some code to clean it up. And schedule a SQL job to run the code regularly.

However, there are mechanisms baked right into SQL Server to manage this more efficiently (step away from scripting everything – devops 😉 )

True enough, you need to run code (once) to clean out all the current duplicates, but going forward a unique filtered index can keep them out.

For this particular project “duplicate data” meant that an ID column should not contain a number already in that column if the Country was ‘UK’ and the Package ID was ‘5’.

Here is a simplified example of my solution …

-- ix_BlockDupCustIDs.sql

IF OBJECT_ID('tempdb..#t1') IS NOT NULL DROP TABLE #t1;
CREATE TABLE #t1 (CustID INT, CountryCode CHAR(2), PackageID INT);

CREATE UNIQUE INDEX ix_BlockDupCustIDs 
ON #t1 (CustID) 
WHERE CountryCode = 'GB' AND PackageID = 5;

INSERT INTO #t1 VALUES (1, 'GB', 5) -- yes
INSERT INTO #t1 VALUES (2, 'GB', 5) -- yes
INSERT INTO #t1 VALUES (1, 'GB', 4) -- yes
INSERT INTO #t1 VALUES (1, 'US', 5) -- yes
--INSERT INTO #t1 VALUES (1, 'GB', 5) -- no, duplicate
--INSERT INTO #t1 VALUES (2, 'GB', 5), (3, 'IR', 1) -- no for both
--UPDATE #t1 SET PackageID = 5 WHERE PackageID = 4 -- nope

SELECT * FROM #t1;

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