例如: 把表 tk_zyt_scenery_order的 字段更新到 t_advs_order中去, 一般可能會這樣寫:

UPDATE t_advs_order SET

 attribute1=(SELECT o.order_state FROM tk_zyt_scenery_order o WHERE o.order_id=`on`),

 attribute2=(SELECT o.order_state FROM tk_zyt_scenery_order o WHERE o.order_id=`on`)

 WHERE EXISTS (SELECT o.order_state FROM tk_zyt_scenery_order o WHERE o.order_id=`on`);

這樣效率比較低下, 優化寫法:

UPDATE t_advs_order a INNER JOIN tk_zyt_scenery_order s ON s.order_id=a.`on` SET

 a.attribute1=s.order_id,

 a.attribute2=s.order_id;