CODEWITHSUNDEEP
mysqlsqljoin
pennstatephil
pennstatephil

Reputation: 1653

sql self join on multiple attributes

I have a (legacy) table that has columns in it:

bug_num   build_id    closed_to
1         3            NULL
2         4            NULL
3         NULL         1
4         3            NULL
5         NULL         2

I want to write a query where it will select all bugs from a specific build, and all bugs that were closed to a bug in that build. So, if I wanted to do it for build 3, it would include #s 1 and 4 (since they're in build 3) and also 3, since it was closed to a bug in build 3 (1).

I thought I was close with:

SELECT stat.bug_num, 
       stat.build_id 
FROM   bug_status stat 
       JOIN bug_status stat2 
         ON stat2.closed_to = stat.bug_num 
WHERE  stat.build_id = 3;

...but it doesn't seem to be giving me the desired result. Thanks for your help!

Upvotes: 0

Views: 1680

Answers (4)

knittl
knittl

Reputation: 265341

You are not including stat2.build_id in your WHERE clause (and I think your ON columns taken from the wrong tables):

SELECT stat.bug_num, stat.build_id
FROM bug_status stat
LEFT JOIN bug_status stat2
ON stat.closed_to = stat2.bug_num
WHERE stat.build_id = 3 OR stat2.build_id = 3

Upvotes: 2

ruakh
ruakh

Reputation: 183381

SELECT stat.bug_num,
       stat.build_id
  FROM bug_status  stat
 WHERE stat.build_id = 3
    OR stat.closed_to IN
        ( SELECT stat2.bug_num
            FROM bug_status  stat2
           WHERE stat2.build_id = 3
        )
;

(It's also possible to do this with a JOIN, or with a JOIN and a UNION, but I believe the above is the most intuitive way.)

Edited to add: Here is a MySQL transcript demonstrating the above:

mysql> create table bug_status
    -> (bug_num numeric, build_id numeric, closed_to numeric);
Query OK, 0 rows affected (0.01 sec)

mysql> insert into bug_status values (1, 3, null);
Query OK, 1 row affected (0.00 sec)

mysql> insert into bug_status values (2, 4, null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into bug_status values (3, null, 1);
Query OK, 1 row affected (0.00 sec)

mysql> insert into bug_status values (4, 3, null);
Query OK, 1 row affected (0.00 sec)

mysql> insert into bug_status values (5, null, 2);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT stat.bug_num,
    ->        stat.build_id
    ->   FROM bug_status  stat
    ->  WHERE stat.build_id = 3
    ->     OR stat.closed_to IN
    ->         ( SELECT stat2.bug_num
    ->             FROM bug_status  stat2
    ->            WHERE stat2.build_id = 3
    ->         )
    -> ;
+---------+----------+
| bug_num | build_id |
+---------+----------+
|       1 |        3 |
|       3 |     NULL |
|       4 |        3 |
+---------+----------+
3 rows in set (0.00 sec)

Edited to add, since the IN (...) approach doesn't seem to work in the OP's version of MySQL: Here is an alternative query that gives the same result:

SELECT stat.bug_num,
       stat.build_id
  FROM bug_status  stat
  LEFT
 OUTER
  JOIN bug_status  stat2
    ON stat.closed_to = stat2.bug_num
 WHERE stat.build_id = 3
    OR stat2.build_id = 3
;

Upvotes: 2

Branko Dimitrijevic
Branko Dimitrijevic

Reputation: 52117

This query...

SELECT *
FROM bug_status t1
WHERE
    build_id = 3
    OR EXISTS (
        SELECT *
        FROM bug_status t2
        WHERE
            t2.build_id = 3
            AND t1.closed_to = t2.bug_num
    )

...produces the following result:

bug_num   build_id    closed_to
1         3           NULL
3         NULL        1
4         3           NULL

In plain English: select the rows such that:

  • build_id = 3
  • or there is a related row with build_id = 3.

Upvotes: 0

nadime
nadime

Reputation: 145

Why not:

DECLARE  @build_id int = <the build id>

SELECT   stat.bug_num, stat.build_id, stat.closed_to
FROM     bug_status stat
WHERE    stat.build_id = @build_id 
   OR    stat.closed_to = @build_id

?

Upvotes: 0

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