选择表中所有条目的更新表

Question

在我的场景中，我从条件为真的表中选择所有条目，将其放入向量中并通过循环使用更新语句，并传递向量的值。 有用。

SELECT * FROM MAP AS A WHERE EXISTS  
(SELECT (X, Y) FROM MAP AS B WHERE B.X = A.X + 1 AND B.Y = A.Y ) AND EXISTS     
(SELECT (X, Y) FROM MAP AS C WHERE C.X = A.X - 1 AND C.Y = A.Y ) ;

for...
UPDATE MAP SET VAL = 2 WHERE X = ? AND Y = ?; 
...

但是我想尝试使用单个语句来完成此目标，尽管我们可以使用select语句更新表，但是在我的情况下，选择一条记录之前需要检查2个键，因此我无法放置x或y在一起的条件。

UPDATE MAP SET USED = 1 WHERE EXISTS (
SELECT * FROM MAP AS A WHERE EXISTS  
(SELECT (X, Y) FROM MAP AS B WHERE B.X = A.X + 1 AND B.Y = A.Y ) AND EXISTS     
(SELECT (X, Y) FROM MAP AS C WHERE C.X = A.X - 1 AND C.Y = A.Y ) );

当我将上述条件放在哪里时，它会更新所有条目。 如何在一个查询中更新表？

Answer 1

您的子查询的问题在于它没有引用UPDATE语句中的表（ MAP ）。

只需删除MAP AS A子查询并直接引用MAP （ UPDATE不允许使用表别名）：

UPDATE MAP
SET USED = 1
WHERE EXISTS (SELECT 1 FROM MAP AS B WHERE B.X = MAP.X + 1 AND B.Y = MAP.Y)
  AND EXISTS (SELECT 1 FROM MAP AS C WHERE C.X = MAP.X - 1 AND C.Y = MAP.Y)

Answer 2

由于您已经验证了子查询返回了要更新的行，因此更新应如下所示：

UPDATE MAP SET USED = 1 
WHERE (X,Y) IN (
SELECT X, Y FROM MAP AS A WHERE EXISTS  
(SELECT X, Y FROM MAP AS B WHERE B.X = A.X + 1 AND B.Y = A.Y ) AND EXISTS     
(SELECT X, Y FROM MAP AS C WHERE C.X = A.X - 1 AND C.Y = A.Y ) );