MariaDB [civicrm]> explain SELECT email FROM civicrm_email JOIN civicrm_contact ON civicrm_email.contact_id = civicrm_contact.id JOIN civicrm_contribution ON civicrm_contact.id = civicrm_contribution.contact_id INNER JOIN ccogdill.GCOrderID0315 ON civicrm_contribution.trxn_id LIKE CONCAT('%', ccogdill.GCOrderID0315.id, '%') WHERE civicrm_email.email IS NOT NULL;