使用MySQL 4.0版或更高更新您可以通過加入兩個或多個表一起一表;通過加入兩個表連同您可以更新一個表的記錄在相關領域的總部設在另一個表。
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;
新聞熱點
疑難解答