Combine two queries into one in same table (same columns/different rows)

Question

For a messaging system, I'm trying to mark the appropriate to_del and from_del fields for employee 2.

Here is before employee 2 deletes messages:

company_id | to | from | to_del | from_del
    1        4     2       0         0
    1        2     4       0         0

Here is after employee 2 deletes messages:

company_id | to | from | to_del | from_del
    1        4     2       0         1
    1        2     4       1         0

I have to run 2 queries for this to work:

UPDATE messages SET from_del='1' WHERE company_id=1 AND from=2
UPDATE messages SET to_del='1' WHERE company_id=1 AND to=2

Is there anyway to merge these 2 queries into 1 more efficient query? Something like:

UPDATE messages SET from_del='1',to_del='1' WHERE company_id=1 AND (from=2 OR to=2)

This single query's issue is that it marks all 4 delete fields as '1'. Any ideas on how to get a single efficient query to act like the 2 above queries?

Answer 1

Sounds like a job for case ...

update messages
   set from_del = case when from = 2 then 1 else from_del end
     , to_del = case when to = 2 then 1 else to_del end
 where company_id = '1'

You're updating columns that don't need to be this way, but you're only performing one update not multiple as you would with multiple queries.

I dislike the use of from and to as column names... It just asking for confusion...

Answer 2

If you're performing an update that requires two different WHERE clauses, then unfortunately you will have to perform two queries. If you are worried about performance, you could always batch them in a single TRANSACTION .