Question

I’m a bit not understanding – on update, insert, delete queries result_metadata returns false? Because:

$meta = $stmt->result_metadata();
if($meta === false){
    throw new Exception(...));
}

throws the exception when i try to run update, insert or delete query. But it should be false only on error. (from php manual)

Answer 1

The function is intended to return data about the data you’ve just made a query about (metadata!). The action of inserting rows, updating rows, and deleting rows usually doesn’t actually return a result set.

(At least not in MySQL. In certain other databases, like Postgres, there’s the RETURNING clause…)

From the comments on the mysqli_stmt_result_metadata manual page:

If result_metadata() returns false but error/errno/sqlstate tells you no error occurred, this means your query is one that does not produce a result set, i.e. an INSERT/UPDATE/DELETE query instead of a SELECT query.

This is stated in the documentation where it says "If a statement passed to mysqli_prepare() is one that produces a result set, mysqli_stmt_result_metadata() returns the result object", but it might not be clear to everyone what this entails exactly.