MySQL SELECT语句问题

Question

I have the following query which returns 2 tuples

SELECT bar_id, bar_name, town_name, bar_telephone, subscription_type_id, pic_type
FROM towns, subscriptiontype, regions, bar
LEFT JOIN barpictures bp ON bar.bar_id = bp.bar_id_fk
WHERE town_id = town_id_fk
AND bar.test_field = 0
AND subscription_type_id = subscription_type_id_fk
AND region_id = region_id_fk
AND (type like 'logo%' OR type IS NULL) 

The main difference between the tuples is that one has 'type' = logo and the other tuple has 'type' = logo_large. I need that instead of having two tuples, I need that I have 2 type attributes, one holding the "logo" and the other the "logo_large"

eg

bar_id, bar_name, town_name, bar_telephone, subscription_type_id, pic_type1, pic_type2

is this possible?

Answer 1

Yes, it is possible:

SELECT ..., subscription_type_id,
    MAX(IF(type='logo',type,NULL)) as pic_type1,
    MAX(IF(type='logo_large',type,NULL)) as pic_type2
...
GROUP BY bar_id;

The idea is to use aggregating functions to merge the rows and select only the value that matches your condition (for non-matching rows the aggregating function should return null)