Update table for all entries from select statement

Question

In my scenario, i select all the entries from a table where the condition is true, put it into a vector and use an update statement through a loop, passing the vector's values. It works.

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 = ?; 
...

But i wanted to try and use a single statement to complete this objective, while we can update a table using a select statement, in my scenario there are 2 keys that need to checked before selecting a record, so i'm not able to put a where condition for x or y together.

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 ) );

When i put a where exists condition like above, it updates all the entries. How do i update the table in one query ?

Answer 1

The problem with your subquery is that it does not refer to the table ( MAP ) in the UPDATE statement.

Just drop the MAP AS A subquery and refer to MAP directly ( UPDATE does not allow table aliases):

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

Since you've verified the subquery is returning the rows you want to update, your update should then look something like this:

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 ) );