Query using CASE WHEN

Question

I am trying to write a query like this and I am getting an error. It is my first time using case, so that's where I believe the problem to be.

UPDATE my_table 
       CASE
              WHEN downloads IS NULL THEN 
              SET    downloads = 1 
              ELSE 
              SET    downloads + 1 
       END
WHERE  attachment_id = 8990 
AND    parent_post_id = 9221 
OR     attachment_id = 9211 
AND    parent_post_id = 383

Answer 1

You can rewrite it as below

UPDATE my_table 
SET downloads = CASE WHEN downloads IS NULL THEN  1 
                ELSE downloads + 1 END
WHERE attachment_id = 8990 
AND (parent_post_id = 9221 
OR attachment_id = 9211 )
AND parent_post_id = 383

Also you need to group your or condition in () in order to match 9211 against parent_post_id and attachment_id with or operation,also there is confusing conditions you have in your query how parent_post_id and attachment_id can be equal to 2 values at same time may be you are looking for

WHERE (attachment_id = 8990  AND parent_post_id = 9221 ) 
OR (attachment_id = 9211  AND parent_post_id = 383)

Answer 2

update s syntax is update table set col=value where condition . Using case doesn't change that. case can only be used to return an expression, so:

UPDATE my_table 
SET    downloads = CASE WHEN downloads IS NULL THEN 1 ELSE downloads + 1 END 
WHERE  attachment_id = 8990 AND
       parent_post_id = 9221 OR
       attachment_id = 9211 AND 
       parent_post_id = 383