Why Does My MySQLi Code Generate a 'Commands Out of Sync' Error?

Why is mysqli giving a "Commands out of sync" error?

When trying to execute MySQL queries simultaneously, you may encounter the "Commands out of sync" error. This occurs when the MySQL client detects that there are still rows to be fetched from an ongoing query while attempting to execute a new one.

Cause of the Error

The MySQL client demands that all rows from a query be fetched before initiating a new query. This prevents data corruption and ensures that the client's state remains synchronized with the server's.

Resolving the Issue

1. Pre-Fetching the Results

You can use mysqli_store_result() to retrieve all rows from the outer query. This instructs the MySQL client to buffer the results, allowing you to execute subsequent queries without interference.

2. Fetch All Results

Alternatively, you can utilize mysqli_result::fetch_all(), which returns the full result set as a PHP array. This enables you to iterate through the array without having to perform any further queries.

Special Case: Stored Procedures

Stored procedures can return multiple result sets, each with its own rows. To handle this scenario, you should employ mysqli_multi_query(). This method initiates the stored procedure and loops through its result sets until there are no more using mysqli_next_result().

Hierarchical Data Modeling Alternative

In scenarios where you have hierarchical data represented in a flat table, consider using a different data modeling approach to simplify querying.

CodeIgnitor 3.0.3 Workaround for mysqli_next_result()

For individuals using CodeIgnitor 3.0.3 and experiencing this error, a workaround exists in the mysqli_driver.php file. Specifically, on line 262, modify the _execute() method as follows:

protected function _execute($sql)
{
    $results = $this->conn_id->query($this->_prep_query($sql));
    @mysqli_next_result($this->conn_id); // Fix 'command out of sync' error
    return $results;
}

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