What is the WordPress `wpdb::last_error` and `SAVEPOINTDB` pattern for nested database transactions?

Question

WordPress Expert — Hard

What is the WordPress `wpdb::last_error` and `SAVEPOINTDB` pattern for nested database transactions?

Accepted Answer

MySQL doesn't support nested transactions; SAVEPOINT allows partial rollback. WordPress developers must manually handle transactions using $wpdb->query('START TRANSACTION') and $wpdb->query('SAVEPOINT'). Checking $wpdb->last_error after each query ensures proper error handling.