How to Resolve the 'Commands Out of Sync' Error in MySQLi?

Commands Out of Sync Error in MySQLi

Your code, which involves multiple MySQLi queries, encounters the "Commands out of sync" error. This error occurs because the MySQL client prohibits executing new queries while there are still rows to be fetched from an in-progress query.

Understanding the Issue

The MySQL client implements a strict protocol that ensures queries are executed in sequence. When you have nested queries or procedures that return multiple result sets, the protocol dictates that you fetch all rows from a result set before executing the next query. However, in your case, you are attempting to execute a new query while there are still rows to be fetched from the previous one.

Solutions

There are two main approaches to resolve the issue:

1. Pre-fetch Results: Use mysqli_store_result() or mysqli_result::fetch_all() to buffer the results of the outer query in the MySQL client. This will allow you to execute further queries without encountering the error.
2. Handle Multiple Result Sets: If your stored procedure returns multiple result sets, you need to use mysqli_multi_query() and loop until mysqli_next_result() indicates no more results. This ensures you comply with the MySQL protocol.

Alternate Data Storage Consideration

For hierarchical data, you may want to consider storing it differently to simplify queries. For example, you could use adjacency lists or nested sets models.

Additional Notes

In CodeIgnitor 3.0.3, you can resolve the "Commands out of sync" error by modifying the _execute() method in system/database/drivers/mysqli/mysqli_driver.php.

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