MySQL UPDATE与同一表的SUBQUERY [英] MySQL UPDATE with SUBQUERY of same table
问题描述
我正在使用一个复杂的MySQL数据库表来收集表单数据.我在下面名为 test 的示例表中简化了布局:
I am working with a complex MySQL database table that collects form data. I have simplified the layout in an example table called test below:
|FormID|FieldName| FieldValue |
| 1 | city | Houston |
| 1 | country | USA |
| 2 | city | New York |
| 2 | country |United States|
| 3 | property| Bellagio |
| 3 | price | 120 |
| 4 | city | New York |
| 4 |zip code | 12345 |
| 5 | city | Houston |
| 5 | country | US |
通过phpMyAdmin,我需要对某些表进行全局更新,特别是我想使用 FieldName将所有 FieldValue 条目 update 到美利坚合众国" 国家/地区",该国家/地区与 FieldName "city"和 FieldValue 休斯顿"具有相同的 FormID .
Through phpMyAdmin I need to make global updates to some tables, specifically I want to update all FieldValue entries to "United States of America" with the FieldName "country" that have the same FormID as the FieldName "city" and the FieldValue "Houston".
通过使用SUBQUERY或使用INNER JOIN,我可以使用SELECT语句轻松显示这些条目:
I can easily display these entries with a SELECT statement by either using a SUBQUERY or by using an INNER JOIN:
SELECT FieldValue
FROM test
WHERE FormID
IN (
SELECT FormID
FROM test
WHERE FieldName = "city"
AND FieldValue = "Houston"
)
AND FieldName = "country"
或者:
SELECT a.FieldValue
FROM test a
INNER JOIN test b ON a.FormID = b.FormID
WHERE a.FieldName = "country"
AND b.FieldName = "city"
AND b.FieldValue = "Houston"
但是,我尝试编写我的 UPDATE 语句时,出现某种形式的MySQL错误,指示我无法在子查询或内部引用同一表加入或联盟方案.我什至创建了一个视图,并试图在update语句中引用它,但没有解决方法. 有人知道如何帮助我吗?
However I try to compose my UPDATE statement I get some form of MySQL-error indicating that I cannot reference the same table in either a subquery or inner join or union scenario. I have even created a view and tried to reference this in the update statement, but no resolve. Does anyone have any idea how to help me?
推荐答案
您必须使用临时表,因为您无法更新用于选择的内容.一个简单的例子:
You have to use a temporary table, because you can't update something you use to select. A simple exemple:
这不起作用:
UPDATE mytable p1 SET p1.type= 'OFFER' WHERE p1.parent IN
(SELECT p2.id from mytable p2 WHERE p2.actu_id IS NOT NULL);
这将完成工作:
UPDATE mytable p1 SET p1.type= 'OFFER' WHERE p1.parent IN
(SELECT p2.id from (SELECT * FROM mytable) p2 WHERE p2.actu_id IS NOT NULL);
"from(SELECT * FROM mytable)p2"将创建您的表的临时副本,这将不受更新的影响
"from (SELECT * FROM mytable) p2" will create a temporary duplicate of your table, wich will not be affected by your updates
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