Question

I am getting completely crazy with this query and was wondering if there is a genius out there for whom this would be a mere child’s play…?

This query should suggest random users to logged in users, whereas the relationship between the logged-in user and the suggested users must not be blocked in one of those ways:

• by continents
• by countries
• by age-range
• by gender
• by id (blocker<->blockee)

Table structure

user

id | username | country_id_home | timestamp_lastonline | gender | birthdate | allow_gender | age_min | age_max | ...

comment: birthdate is in mysql-date format (YYYY-MM-DD), gender (0=female,1=male), allow_gender (0=both, 1=female, 2=male)

countries

country_id | name | continent_id | ...

cities

id | city_real | ...

comment: loc_id_home in table user matches id in cities

blocked_countries

id | user_id | country_id | ...

blocked_continents

id | user_id | continent_id | ...

blocked_user

id | user1_id | user2_id | ...

comment: user1 is “blocker”, user2 is “blockee”

The query I have till now is:

SELECT u.id AS user_id, u.username, u.fname, u.country_id_home, u.timestamp_reg, u.timestamp_upd, u.timestamp_lastonline, u.online_status, u.gender, u.birthdate, u.prof_pic,

(SELECT name FROM countries co WHERE co.country_id=u.country_id_home) AS country_name,
(SELECT city_real FROM cities ci WHERE ci.id=u.loc_id_home) AS city ,
(SELECT region_name FROM regions r WHERE r.id=u.region_id_home) AS region,
(SELECT region_short FROM regions r WHERE r.id=u.region_id_home) AS region_short

FROM user_d1 u 

LEFT JOIN (
SELECT DISTINCT user2_id AS blockee_id
FROM blocked_user
WHERE user1_id = :user1_id1
)this_user_blocked ON u.id = this_user_blocked.blockee_id

LEFT JOIN (
SELECT DISTINCT user1_id AS blocker_id
FROM blocked_user
WHERE user2_id = :user1_id2
)blocked_this_user ON u.id = blocked_this_user.blocker_id

WHERE 

(allow_gender=0 OR allow_gender=:user1_allow_gender)

AND age_min<=:user1_age1
AND age_max>=:user1_age2


AND prof_status<>2

AND this_user_blocked.blockee_id IS NULL AND blocked_this_user.blocker_id IS NULL 

AND NOT EXISTS (SELECT 1 FROM blocked_countries bc WHERE bc.user_id=u.id AND bc.country_id =:user1_country)
AND NOT EXISTS (SELECT 1 FROM blocked_countries bc WHERE bc.user_id=:user1_id3 AND bc.country_id = u.country_id_home)

AND EXISTS (
    SELECT 1 FROM user_d1 u2 
    WHERE u2.id=:user1_id4
    AND (u2.allow_gender=0 OR u2.allow_gender=(u.gender+1))
    AND age_min<=(DATEDIFF(NOW(),u.birthdate))
    AND age_max>=(DATEDIFF(NOW(),u.birthdate))
    AND prof_status<>2
    )

LIMIT 0,6

Without the last AND EXISTS... the result set is not empty, however like this it does always return no results. Yet blocked by continents is not included and it is not yet ordered by timestamp_lastonline…

What am I doing wrong in the last AND EXISTS...? Should it rather be done with a JOIN? I’ve tried that too, but it gave an empty result as well…

I have stored all necessary variables from the logged in user in SESSION-variables… if you find anything else in the query that could be done in a better way I’d be very happy for your help too!

Thank you very much in advance!

Answer 1

I think it’s because of DATEDIFF, which returns the numbers of days between two dates and not the number of years. Therefore DATEDIFF is probably always greater than age_max.

EDIT: You could do something like this instead:

...
AND DATE_SUB(NOW(), INTERVAL age_max YEAR) <= u.birthdate
AND DATE_SUB(NOW(), INTERVAL age_min YEAR) >= u.birthdate
...