You can't specify target table 'table_name' for update in FROM clause - How to solve MySQL error: Unable to update target table in FROM clause

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During the development of MySQL database, we sometimes encounter the following error message: You can't specify target table 'table_name' for update in FROM clause surface). This error usually occurs when we use an UPDATE statement with a subquery, especially when the target table that needs to be updated is referenced in the subquery.

This article will introduce the cause of this error and provide solutions and specific code examples.

First, let us look at an example to reproduce this error:

UPDATE table_name
SET column_name = value
WHERE column_name IN (SELECT column_name FROM table_name WHERE condition);

In the above code, we try to update the table named table_name and use a subquery as the WHERE condition. However, in MySQL, updating the target table directly in the FROM clause is not allowed.

The reason for this error lies in the order in which MySQL executes UPDATE statements. The execution sequence of MySQL is to first obtain data from the FROM clause, then filter and perform update operations based on the WHERE condition. Since we reference the target table that needs to be updated in the subquery, this causes a conflict because we cannot reference the target table while updating it.

In order to solve this problem, we need to modify the code. The following are several common solutions:

Solution 1: Use INNER JOIN

UPDATE table_name
INNER JOIN (SELECT column_name FROM table_name WHERE condition) AS temp_table
ON table_name.column_name = temp_table.column_name
SET table_name.column_name = value;

In the above code, we connect the target table and the result set of the subquery through INNER JOIN, and pass WHERE condition to filter. In this way, we can reference the results of the subquery during the update process without error messages.

Solution 2: Use a temporary table

CREATE TEMPORARY TABLE temp_table
SELECT column_name FROM table_name WHERE condition;

UPDATE table_name
SET column_name = value
WHERE column_name IN (SELECT column_name FROM temp_table);

In this solution, we first store the result set of the subquery in a temporary table, and then use the temporary table to perform the update operation. This way, you avoid the problem of referencing itself when updating the target table.

Solution 3: Use subquery as field

UPDATE table_name
SET column_name = (
    SELECT column_name FROM table_name WHERE condition
)
WHERE column_name = value;

In this solution, we update the subquery as field value. By using a subquery as a field in the UPDATE statement, we can bypass the limitations of updating the target table directly in the FROM clause.

To summarize, when we encounter the error message You can't specify target table 'table_name' for update in FROM clause in MySQL, it means that we referenced the target table being updated in the UPDATE statement. In order to solve this problem, we can use INNER JOIN, a temporary table, or use a subquery as a field to perform update operations.

I hope the above solutions and code examples will help you solve this MySQL error problem! If you have any other questions, please feel free to continue asking.

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