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.namewhere 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; |
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