将WHERE条件添加到3表LEFT JOIN查询中...？

Question

I'm working my way through the php world but still finding my feet. I've written a query that works nicely for collecting what i need from mysql, but I just cannot get it to work with a WHERE condition. Any help would be much appreciated!

Here's my working query without the WHERE condition:

SELECT foo.*, users.name, SUM(bar.amt) Total FROM foo 
     LEFT JOIN bar ON foo.id = bar.foo_id 
     LEFT JOIN users ON foo.foo_owner_id = users.id 
     LIMIT 16 GROUP BY foo.id"

And here's what I think should work to add the WHERE condition but doesn't work...

SELECT foo.*, users.name, SUM(bar.amt) Total FROM foo 
     WHERE foo.category = $var LEFT JOIN bar ON foo.id = bar.foo_id 
     LEFT JOIN users ON foo.foo_owner_id = users.id LIMIT 16 GROUP BY foo.id"

Any and all suggestions are welcome, thanks!!

Answer 1

非常简单：所有WHERE条件都应放在所有JOIN之后。

Answer 2

You need to put the WHERE clause after all the joined tables. Hence

SELECT foo.*, users.name, SUM(bar.amt) Total
FROM foo
    LEFT JOIN bar ON foo.id = bar.foo_id
    LEFT JOIN users ON foo.foo_owner_id = users.id
WHERE foo.category = $var
GROUP BY foo.id
LIMIT 16;

You probably also want the LIMIT clause to be last.

Answer 3

use

SELECT 
foo.*, 
users.name, 
SUM(bar.amt) Total 
FROM foo 
LEFT JOIN bar ON foo.id = bar.foo_id 
LEFT JOIN users ON foo.foo_owner_id = users.id 
WHERE foo.category = $var 
GROUP BY foo.id
LIMIT 16 

Answer 4

when you are using left or right join then always use where clause after joins.

SELECT foo.*, users.name, SUM(bar.amt) Total
   FROM foo
   LEFT JOIN bar ON foo.id = bar.foo_id
   LEFT JOIN users ON foo.foo_owner_id = users.id
   WHERE foo.category = $var
   GROUP BY foo.id
   LIMIT 16;

even if u want order by id etc use it before LIMIT