先來幾個簡單的示例
Solution 1: 1列
update student s, city c
set s.city_name = c.name
where s.city_code = c.code;
Solution 2: 多個列
update a, b
set a.title=b.title, a.name=b.name
where a.id=b.id
Solution 3: 子查詢
update student s set city_name = (select name from city where code = s.city_code);
我們再來看幾個負責寫的
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(yōu)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;
