Question

Is there any way in the SQL language or in MySQL (or other DBMA) to transfer a value from one cell to another? For example, say there is a table called user_cars with the following structure:

|id| |user_name| |num_cars| 

Bob has 5 cars, and John has 3 cars. Is there any way to in one query subtract 2 cars from Bob and add 2 to John? I know this can be done with two update queries, but I’d just like to know if there was a more efficient way.

Answer 1

For Oracle you could do this. Don’t know if there is an equivalent in mysql. Obviously this particular statement is very specific to the example you stated.

 UPDATE user_cars    SET num_cars = num_cars +                      CASE WHEN user_name='Bob' THEN -2                           WHEN user_name='John' THEN +2                      END    WHERE user_name IN ( 'Bob', 'John' )