How to Solve the 'You Can't Specify Target Table for Update in FROM Clause' Error in MySQL?

Resolving the MySQL "You can't specify target table for update in FROM clause" Error

Encountering the error "You can't specify target table for update in FROM clause" during a MySQL UPDATE query? This typically happens when you try to reference the table being updated within a subquery. Let's look at a common scenario:

UPDATE pers P
SET P.gehalt = P.gehalt * 1.05
WHERE (P.chefID IS NOT NULL
OR gehalt <p>...This approach fails because MySQL prohibits referencing the updated table (pers) inside its own subquery.</p><h2 id="The-Solution-Employing-a-Temporary-Table-or-JOIN">The Solution: Employing a Temporary Table (or JOIN)</h2><p>The solution involves creating a temporary representation of the table data to avoid directly referencing the `pers` table in the `WHERE` clause.  Here's how:</p>UPDATE pers P
SET P.gehalt = P.gehalt * 1.05
WHERE (P.chefID IS NOT NULL
OR gehalt <p>This method uses a `SELECT` statement to create a temporary dataset.  This allows the `WHERE` clause to reference the data without directly referencing the `pers` table being updated.</p><h2 id="Alternative-Using-a-JOIN">Alternative: Using a JOIN</h2><p>Another effective method is to use a `JOIN` instead of a subquery:</p>UPDATE pers p
INNER JOIN (SELECT chefID, gehalt FROM pers) AS temp ON p.chefID = temp.chefID AND p.gehalt = temp.gehalt
SET p.gehalt = p.gehalt * 1.05
WHERE p.chefID IS NOT NULL OR p.gehalt <p>This approach achieves the same result by joining the `pers` table with itself (aliased as `temp`), thereby avoiding the restriction.</p><h2 id="Best-Practices">Best Practices</h2><p>While using `SELECT *` simplifies the example, selecting only necessary columns and adding a `WHERE` clause to your subquery or `JOIN` significantly improves performance.  Always prioritize efficiency in your database operations.</p>

This clarifies the problem and provides alternative solutions. Remember to select only necessary columns for optimal performance.

The above is the detailed content of How to Solve the 'You Can't Specify Target Table for Update in FROM Clause' Error in MySQL?. For more information, please follow other related articles on the PHP Chinese website!