How Can SQL Developers Ensure Unique Row Insertion Under High Load?

Ensuring Unique Row Inserts in SQL Databases Under Pressure

A common challenge for SQL developers is inserting rows without creating duplicates. The traditional method often involves a subquery:

<code class="language-sql">INSERT INTO TheTable
SELECT
    @primaryKey,
    @value1,
    @value2
WHERE
    NOT EXISTS
    (SELECT
        NULL
    FROM
        TheTable
    WHERE
        PrimaryKey = @primaryKey)</code>

Under heavy load, however, this approach can lead to primary key violations, compromising statement atomicity.

To mitigate this, some developers employ locking mechanisms:

<code class="language-sql">INSERT INTO TheTable
WITH
    (HOLDLOCK,
    UPDLOCK,
    ROWLOCK)
SELECT
    @primaryKey,
    @value1,
    @value2
WHERE
    NOT EXISTS
    (SELECT
        NULL
    FROM
        TheTable
    WITH
        (HOLDLOCK,
        UPDLOCK,
        ROWLOCK)
    WHERE
        PrimaryKey = @primaryKey)</code>

But excessive locking significantly impacts performance.

A more efficient strategy, often referred to as the "JFDI" (Just F***ing Do It) method, involves direct insertion with error handling:

<code class="language-sql">BEGIN TRY
   INSERT etc
END TRY
BEGIN CATCH
    IF ERROR_NUMBER() <> 2627
      RAISERROR etc
END CATCH</code>

This avoids nested queries and locking, promoting concurrency under high volume.

Critically, proper indexing is paramount. As highlighted in "Lesson 4" by a seasoned SQL developer, relying solely on subqueries for duplicate prevention is unreliable. A unique index, coupled with appropriate error handling (like catching error 2627), provides automatic duplicate prevention, streamlining the process.

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