How to Insert Data into Multiple MySQL Tables While Handling Auto-Incremented IDs?

Inserting Data into Multiple MySQL Tables

In MySQL, it is not possible to execute a single query to insert data into multiple tables simultaneously. To achieve this, one common approach is to use multiple queries. However, this raises the question of how to assign the auto-incremented user ID from the users table to the userid column in the profiles table.

Solution: Utilizing Transactions and LAST_INSERT_ID()

To seamlessly transfer the auto-incremented ID, we can leverage transactions and the LAST_INSERT_ID() function. Here's a revised code snippet:

BEGIN;
INSERT INTO users (username, password)
VALUES('test', 'test');
INSERT INTO profiles (userid, bio, homepage)
VALUES(LAST_INSERT_ID(), 'Hello world!', 'http://www.stackoverflow.com');
COMMIT;

In this transaction, the first query inserts a record into the users table. The LAST_INSERT_ID() function within the second query retrieves the auto-incremented ID from the first insertion and assigns it to the userid field in the profiles table. The COMMIT statement finalizes the transaction, ensuring both insertions are either completed or aborted.

Additional Considerations

LAST_INSERT_ID() Reset: When the second query inserts records into a table with an auto-increment column, LAST_INSERT_ID() is updated to the new ID. To prevent this, you can stock the initial ID in a MySQL or language-specific variable:

Option 1: MySQL Variable

INSERT ...
SELECT LAST_INSERT_ID() INTO @mysql_variable_here;
INSERT INTO table2 (@mysql_variable_here, ...);

Option 2: Language Variable

INSERT ...
$last_id = mysql_insert_id();
INSERT INTO table2 ($last_id, ...);

Transactions and Interruptions: If query execution is interrupted between queries, you may encounter data inconsistency. To ensure data integrity, you can implement a transaction block around the queries, which guarantees that either all queries are executed or none are.

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