是否可以根据其中一个查询的结果将MySQL查询与多个表组合成一个查询？

Question

The $userid of the currently logged in user is all the is currently available in the PHP code. I want to run a query against the mysql tables to return all of the status updates for myself and for friends ordered by createddate DESC .

MySQL Sample database tables:

[statusupdates]

statusupdateid int(8)  
ownerid int(8)
message varchar(250)
createddate datetime

[friends]

friendid int(8)
requestfrom int(8)
requestto int(8)
daterequested datetime
dateupdated datetime
status varchar(1)

Question: Can I perform a single string query that returns each statusupdates.userid and the statusupdates.message ordered by statusupdates.createddate DESC ?

Or do I have to run a query for each friends record where the $userid is in either the friends.requestfrom or friends.requestto then, run another query for alternate friends.requestfrom or friends.requestto (the one that doesn't include $userid ), then sort all of the results by statusupdate.createddate and then get the statusupdates.message ?

Answer 1

You want to look at MySQL Joins.

I think this may do something like what you're after, but it will almost definitely need debugging!

SELECT DISTINCT s.ownerid, s.message 
FROM statusupdates s 
LEFT JOIN friends f ON ($userid = f.requestfrom) 
LEFT JOIN friends f ON ($userid = f.requestto)
ORDER BY s.createddate;

Answer 2

This is untested, but should work or at least get you in the right direction.

You could use IN() where you get a list of userid s from a sub query. That subquery does a UNION on 2 queries - 1st to get the requestfrom userid s, and 2nd to get the requestto userids . Finally we add an OR to include the current userid.

also, I assume that you also want to filter out where status = 1 , as you don't want updates from those who have not confirmed friendships

SELECT s.ownerid, s.message 
FROM statusupdates s 
WHERE s.ownerid IN (
                   SELECT f1.requestfrom
                   FROM friends f1
                   WHERE f1.requestto = $userid
                   AND f1.status = 1

                   UNION

                   SELECT f2.requestto
                   FROM friends f2
                   WHERE f2.requestfrom = $userid
                   AND f2.status = 1
                   )
OR s.ownerid = $userid
ORDER BY s.createddate DESC

take a look at this sqlFiddle example - http://sqlfiddle.com/#!2/85ea0/3