Question

My table contains these values

Name VARCHAR(50),
Program VARCHAR(50),
 Branch VARCHAR(30),
TotalP INT,
 TotalN INT)

I’ve been trying to INSERT records into this table IF the Name doesn’t already exist. This has probably already been answered on here but when I type something into the search it comes up with 7000+ results and I looked through 100+ and still didn’t find the answer. Any and all help is appreciated.

Answer 1

If you aren’t worried about concurrency, the following would work:

IF NOT EXISTS (
    SELECT 1
    FROM YourTable
    WHERE Name = @Name
)
BEGIN
    INSERT INTO YourTable (Name, Program, Branch, TotalP, TotalN)
    VALUES (@Name, @Program, @Branch, @TotalP, @TotalN)
END

The problem here would be that if two processes attempted to add the same name at the same moment… both would pass the IF NOT EXISTS check, and then both would INSERT.

To prevent this, you can either add a unique constraint to the name column, which would cause one of the inserts to fail, or you could lock the table in your NOT EXISTS check using WITH (UPDLOCK, HOLDLOCK), which would reduce concurrency but not raise any errors.

EDIT:

If the values that you want are from a SELECT statement, the following would work:

INSERT INTO YourDestinationTable (Name, Program, Branch, TotalP, TotalN)
SELECT st.Name, st.Program, st.Branch, st.TotalP, st.TotalN
FROM 
    YourSourceTable st
    LEFT JOIN YourDestinationTable dt
        ON dt.Name = st.Name
WHERE 
    dt.Name IS NULL
    -- Add in any other conditions for YourSourceTable here...

This will insert the row from YourSourceTable if the row is not found in YourDestinationTable… implemented using a LEFT JOIN and IS NULL check.

This has the same caveats as before… if two processes run this statement simultaneously, you can end up with duplicate name values; either add a unique constraint on name, or perform a (UPDLOCK, HOLDLOCK) on the row in the destination table that you’re testing for existence inside of a transaction:

BEGIN TRANSACTION
    IF NOT EXISTS (
        SELECT 1
        FROM 
            YourSourceTable st
            JOIN YourDestinationTable dt WITH (UPDLOCK, HOLDLOCK) 
                ON dt.Name = st.Name
        -- WHERE 
            -- Add in any other conditions for YourSourceTable here...
    )
    BEGIN
        INSERT INTO YourDestinationTable (Name, Program, Branch, TotalP, TotalN)
        SELECT Name, Program, Branch, TotalP, TotalN
        FROM YourSourceTable st
        -- WHERE 
        -- Add in any other conditions for YourSourceTable here...
    END
COMMIT