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1MYSQL How do I update a table only if a unique key pair of two columns does not exist in another table?
2**Subject_Table**              
3
4SID   Subject   Total_Votes          
51     Cows      5     
62     Chickens  3     
7
8
9**Vote_Table**
10
11VID   Subject   User    Voteup           
121     Cows      John    1
13	
14ALTER TABLE Vote_Table ADD UNIQUE limitvote(Subject,User);
15	
16$sql="INSERT INTO Vote_Table (Subject, User,Voteup) VALUES ('$Subject', '$User', '$Voteup') ON DUPLICATE KEY UPDATE up=1";
17$q = "UPDATE Subject_Table SET Total_Votes = $votes_up= //current votes plus 1;
18	
19UPDATE Subject_Table
20   SET Total_Votes = Total_Votes + 1
21 WHERE Subject = ...
22   AND NOT EXISTS
23        ( SELECT 1
24            FROM Vote_Table
25           WHERE Subject = ...
26             AND User = ...
27        )
28;
29	
30CREATE VIEW Subject_View AS
31SELECT Subject,
32       COUNT(1) AS Total_Votes
33  FROM Vote_Table
34 GROUP
35    BY Subject
36;