How Can I Update a Specific Range of Rows in MySQL Using a LIMIT Clause?

MySQL: Query for Updating Records Using a Limit

When working with MySQL, it's possible to encounter scenarios where you need to update a specific range of rows in a table. This article addresses the question of whether it's feasible to use a LIMIT clause in an UPDATE query and provides guidance on how to achieve this.

Syntax Error and Correct Usage

Your initial query attempted to update rows starting from 1001 and the next 1000 records. However, the syntax used is incorrect. In MySQL, the LIMIT clause is used to restrict the number of selected rows, not updated rows. The correct way to update a specific range of rows is through a subquery.

For instance, to update the first 1000 rows with p_id set to 3, you would use the following:

UPDATE `oltp_db`.`users` SET p_id = 3
WHERE id IN (
    SELECT id FROM (
        SELECT id FROM `oltp_db`.`users` 
        ORDER BY id ASC  
        LIMIT 0, 1000
    ) tmp
)

Handling NULL Values

In your second query, you attempted to update rows with p_id set to NULL. However, the query would fail because NULL values cannot be compared to non-NULL values in an equality check. To update rows with NULL p_id values, you can use the IS NULL and COALESCE() functions:

UPDATE `oltp_db`.`users` SET p_id = COALESCE(3, p_id)
WHERE p_id IS NULL

By following these guidelines, you can effectively update specific rows in your MySQL table, even when dealing with NULL values.

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