Update table based on another table

Question

I\'m trying to update a column in a table based on another column in another table.

UPDATE eval e
   SET rank = (SELECT p.desc
                 FROM Position         


        

Answer 1

You need a restriction in the form of a WHERE clause; if you use EXISTS you can based it on you scalar subquery e.g.

UPDATE eval
   SET rank = (
               SELECT p.desc
                 FROM Position p
                WHERE p.id = eval.faculty 
                      AND p.date >= '2011-05-20'
              )
 WHERE EXISTS (
               SELECT *
                 FROM Position p
                WHERE p.id = eval.faculty 
                      AND p.date >= '2011-05-20'
              );

Note the above targets the UPDATE on the base table eval rather than the correlation name e. This makes a lot more sense when you think of an SQL UPDATE in terms of relational assignment i.e. you don't want to assign to e because it (unlike the base table) will go out of scope!