Question

I have table with two columns (varchar from, varchar to). This table represents connections betwen nodes (from node, to node). I want to get all nodes connected from or to node that I specify and nodes connected from or to those nodes. Currently I use query below that gives me proper results but I’m searching for neater solution.

//currently used query specified node "node1"
SELECT tonode as node
FROM conn
WHERE
fromnode
IN
(SELECT tonode as node FROM conn WHERE fromnode="node1"
UNION
SELECT fromnode as node FROM conn WHERE tonode="node1")
UNION
SELECT fromnode as node
FROM conn
WHERE
tonode
IN
(SELECT tonode as node FROM conn WHERE fromnode="node1"
UNION
SELECT fromnode as node FROM conn WHERE tonode="node1")


//create table for conn table
CREATE TABLE `conn` (
  `fromnode` varchar(70) NOT NULL,
  `tonode` varchar(70) NOT NULL,
  PRIMARY KEY (`fromnode`,`tonode`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;
INSERT INTO `conn` (`fromnode`,`tonode`) VALUES
 ('node1','node2'),
 ('node1','node3'),
 ('node3','node2'),
 ('node4','node1'),
 ('node4','node2'),
 ('node4','node5'),
 ('node5','node6'),
 ('node4','node3');

Answer 1

My optimized version:

SET @origin = "node1";
SELECT DISTINCT
 IF(c1.fromnode = @origin,
   IF(c1.tonode = c2.tonode,
     IF(c2.fromnode = @origin, c2.tonode, c2.fromnode),
     IF(c2.tonode = @origin, c2.fromnode, c2.tonode)
   ),
   IF(c1.fromnode = c2.tonode,
     IF(c2.fromnode = @origin, c2.tonode, c2.fromnode),
     IF(c2.tonode = @origin, c2.fromnode, c2.tonode)
   )
 ) AS node
FROM conn AS c1
LEFT JOIN conn AS c2 ON (c1.fromnode = c2.fromnode OR c1.tonode = c2.fromnode OR c1.fromnode = c2.tonode OR c1.tonode = c2.tonode)
WHERE c1.fromnode = @origin OR c1.tonode = @origin;

the DESCRIBE output of your old query:

+----+--------------------+------------+--------+---------------+---------+---------+------------+------+--------------------------+
| id | select_type        | table      | type   | possible_keys | key     | key_len | ref        | rows | Extra                    |
+----+--------------------+------------+--------+---------------+---------+---------+------------+------+--------------------------+
|  1 | PRIMARY            | conn       | index  | NULL          | PRIMARY | 424     | NULL       |    8 | Using where; Using index |
|  2 | DEPENDENT SUBQUERY | conn       | eq_ref | PRIMARY       | PRIMARY | 424     | const,func |    1 | Using where; Using index |
|  3 | DEPENDENT UNION    | conn       | eq_ref | PRIMARY       | PRIMARY | 424     | func,const |    1 | Using where; Using index |
| NULL | UNION RESULT       | <union2,3> | ALL    | NULL          | NULL    | NULL    | NULL       | NULL |                          |
|  4 | UNION              | conn       | index  | NULL          | PRIMARY | 424     | NULL       |    8 | Using where; Using index |
|  5 | DEPENDENT SUBQUERY | conn       | eq_ref | PRIMARY       | PRIMARY | 424     | const,func |    1 | Using where; Using index |
|  6 | DEPENDENT UNION    | conn       | eq_ref | PRIMARY       | PRIMARY | 424     | func,const |    1 | Using where; Using index |
| NULL | UNION RESULT       | <union5,6> | ALL    | NULL          | NULL    | NULL    | NULL       | NULL |                          |
| NULL | UNION RESULT       | <union1,4> | ALL    | NULL          | NULL    | NULL    | NULL       | NULL |                          |
+----+--------------------+------------+--------+---------------+---------+---------+------------+------+--------------------------+

the DESCRIBE output of my query:

+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------------------------------------+
| id | select_type | table | type  | possible_keys | key     | key_len | ref  | rows | Extra                                     |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------------------------------------+
|  1 | SIMPLE      | c1    | index | PRIMARY       | PRIMARY | 424     | NULL |    8 | Using where; Using index; Using temporary |
|  1 | SIMPLE      | c2    | index | PRIMARY       | PRIMARY | 424     | NULL |    8 | Using index                               |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------------------------------------+