从表中选择all甚至为null并加入

Question

I want to SELECT the all rows from meeting table even its null. My table structure:

attandance table:
id  | meeting_id  | person_id | time  
1   | 1           | 12        | 02:02
2   | 1           | 15        | 02:05
3   | 1           | 22        | 02:05
4   | 2           | 1         | 02:20
5   | 2           | 12        | 02:01
6   | 3           | 12        | 02:03

and meeting table:
id  | date       
1   | 15-12-2014           
2   | 17-12-2014   
3   | 19-12-2014
4   | 21-12-2014   

The output should be:

If I SELECT the person_id 12 then it should return:

date       |time
15-12-2014 | 02:02
17-12-2014 | 02:01
19-12-2014 | 02:03
21-12-2014 | NULL

If I SELECT the person_id 1 then it should return:

date       |time
15-12-2014 | NULL
17-12-2014 | 02:20
19-12-2014 | NULL
21-12-2014 | NULL

Answer 1

It is a pretty straightforward outer join between the tables:

select
    m.id,
    m.date
    a.time,
    c.someColumn
from
    meetings m
        left outer join attendance a
            on m.id=a.meeting_id
            and a.person_id=:person
        left outer join someTable c
            on m.id=c.id            

I have written a more detailed answer on these sorts of joins in the question and answer: How can an SQL query return data from multiple tables

Edit: As per the comment by Andrew, the clause for the personID is in the join rather than in a normal where clause because it is an outer join. If the condition was put into the where clause as normal, it would in fact negate the outer join completely.