MySQL query logic - mysql

Question

I have a DB full of deals, and a website which will present just one of these deals if the deal is a featured deal, however I am struggling to get the right logic...
the deal that is shown on the site must
a. be within a valid date range
b. be the most recently added deal to the database
by using the following query, I am able to accomplish this:
"SELECT * FROM deals WHERE datestart < now() AND dateend > now() ORDER BY deals.deal_id DESC"
Great. however... on rare occasions a whole bunch of deals are added at once, so I need some kind of override to specify which one should be 'featured'.
I added a boolean value [featured] and tested the following query:
"SELECT * FROM deals WHERE datestart < now() AND dateend > now() ORDER BY deals.featured DESC"
It worked, but now I need to specify the featured deal, or else the featured deal will be randomly selected? whereas I only want to have it as an override.
SO I need to combine the above 2 scripts somehow.
any ideas?
thanks guys.

Answer 1

Add the boolean comparison to the WHERE clause and limit the number of results to 1. When ordering by the deal_id this will always return the same result.
SELECT *
FROM deals
WHERE datestart < now() AND dateend > now() AND deals.featured IS TRUE
ORDER BY deals.deal_id DESC
LIMIT 1
EDIT:
Here is an alternative so you don't have to add more to the WHERE clause.
SELECT *
FROM deals
WHERE datestart < now() AND dateend > now()
ORDER BY deals.featured DESC, deals.deal_id DESC
LIMIT 1
The order of the ORDER clause is important, if deal_id's are unique, as i presumed they were, the featured boolean would not be used if they were ordered the opposite way round.

Answer 2

If you just want to combine the two queries, you can just combine the where clauses - order by deal_id first, then if there are multiples with the same deal_id, it'll then sub order by whether it's featured or not:
SELECT *
FROM deals
WHERE datestart < Now()
AND dateend > Now()
ORDER BY deals.deal_id DESC,
deals.featured DESC

Answer 3

To get featured deals you need to check for featured IS TRUE and use UNION ALL operation to override it:
SELECT *
FROM deals
WHERE datestart < Now()
AND dateend > Now()
AND featured IS TRUE
ORDER BY deal_id DESC
UNION ALL
SELECT *
FROM deals
WHERE datestart < Now()
AND dateend > Now()
ORDER BY deal_id DESC;

Answer 4

I think what you 're trying to do is the following:
UPDATE deals
SET featured=1
WHERE datestart < now() AND dateend > now()
ORDER BY deal_id DESC
LIMIT 1;
Ok, so now you are trying to update the most recent valid featured deal and mark it as featured. If the rows affected count is 0 then you already have the most recent valid featured deal or there is no valid deal at all in the table (it's your choice how to react to this).
If the rows affected count is 1 then you just found a new one and you need to select it (perhaps to fill it in your site). The select statement:
SELECT *
FROM deals
WHERE datestart < now() AND dateend > now() AND featured=1
ORDER BY deal_id DESC
LIMIT 1;
Ideally you would combine these two queries into only one update-select but no way to do just that at the time.