Question

我正在尝试使用table2中的数据（来自'data'）更新一个table1（'keyword'）中的列，他们在'itemid'上加入。然而，'itemid'在table2中并不是唯一的，我仍然坚持如何从记录中获取与正确的'field'匹配的数据来更新table1，如下表所示：

表1：

|itemid | keywords 
-------------------
|   1   |      
|   2   |      
|   3   |      
-------------------

表2：

|itemid | field     | data              
---------------------------------------------------------
|   1   | author    | Shakespeare           
|   1   | title     | Hamlet            
|   1   | topics    | love, loyalty, treason    
|   2   | author    | Dickens           
|   2   | title     | Christmas Carol       
|   2   | topics    | greed, reconciliation 
|   3   | author    | Melville          
|   3   | title     | Moby-Dick         
|   3   | topics    | madness, immortality, sea 
---------------------------------------------------------

我想要实现的目标是表1：

|itemid | keywords          
-----------------------------------------
|   1   | love, loyalty, treason    
|   2   | greed, reconciliation 
|   3   | madness, immortality, sea 
-----------------------------------------

完成此任务的正确查询是什么？我已经尝试过这些查询，它们不会抛出任何错误，但它们不会更新任何行。

UPDATE table1 AS t1, table2 AS t2 SET t1.keywords=t2.data WHERE t1.itemid=t2.itemid AND t2.field='topics'

UPDATE table1 AS t1
    JOIN table2 AS t2 
    ON t1.itemid=t2.itemid
SET t1.keywords=t2.data 
WHERE t2.field='topics'

UPDATE table1 AS t1, (SELECT itemid, data FROM table2 WHERE field='topics') AS t2 SET t1.keywords=t2.data

我看过这里，发现了许多相关的UPDATE帖子，但似乎都没有解决这个问题。我确信这很简单，我很想念。

Answer 1

UPDATE table1 AS t1
SET t1.keywords = 
    ( SELECT t2.data 
      FROM table2 AS t2 
      WHERE t1.itemid = t2.itemid 
        AND t2.field='topics'
    )

Answer 2

UPDATE table1 t1, table2 t2
SET t1.keywords = t2.data
WHERE t1.itemid = t2.itemid
  AND t2.field = 'topics'

从表1到表2的UPDATE字段，其中连接它们的字段在表2中不是唯一的

2 个答案: