How to avoid Duplicate values for INSERT in SQL?

Question

I have one table named:

Delegates

This table has four fields:

ID(Auto increment, Primary)
MemberNo, FromYr, ToYr


        

Answer 1

Try this, (I have not verified)

INSERT INTO Delegates ([MemNo],[FromYr],[ToYr]) values(@MemNo, @FromYr,@ToYr)
where @MemNo not in 
(
    SELECT MemNo FROM words WHERE FromYr = @FromYr
)

Answer 2

Just add a unique index on that column, then inserting duplicates will cause an error. You can then error handle it if it needs to fail gracefully

Answer 3

Before inserting check if there is a record with the same values:

if not exists (select * from Delegates d where d.FromYr = @FromYr and d.MemNo = @MemNo)
    INSERT INTO Delegates ([MemNo],[FromYr],[ToYr]) values(@MemNo, @FromYr,@ToYr)

Answer 4

You can avoid inserting duplicates with this simple, one line of code:

INSERT INTO Delegates (MemNo, FromYr, ToYr) SELECT @MemNo, @FromYr, @ToYr WHERE NOT EXISTS (SELECT 1 FROM Delegates d WHERE d.MemNo=@MemNo AND d.FromYr=@FromYr)

If it's a high load environment where another command could insert the duplicate while this command is executing, you can use the WITH(HOLDLOCK) hint.

Answer 5

Use MERGE

MERGE INTO Delegates D
USING (values(@MemNo, @FromYr,@ToYr)) X ([MemNo],[FromYr],[ToYr])
ON (insert unique key join)
WHEN NOT MATCHED BY TARGET THEN
INSERT ([MemNo],[FromYr],[ToYr]))
VALUES (X.[MemNo],X.[FromYr],X.[ToYr]);

Answer 6

make a stored procedure that will first make a check on the whether the values are already contained in the DB. if they arent you will do your insert. If they simply ignore it