Question

My Tables:

CREATE TABLE `binary` (
  `binaryid` int(15) unsigned NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`binaryid`)
);

CREATE TABLE `binarycollection` (
  `binaryid` int(10) unsigned NOT NULL,
  `collectionid` int(10) unsigned NOT NULL,
  UNIQUE KEY `collectionid` (`collectionid`,`binaryid`),
  KEY `binaryid` (`binaryid`)
);

In the binary table there can only exist one record to a binaryid.
The binarycollection table ties the binary to multiple collections.

What I need to do is make a query that will select all rows in binary that have exactly 1 relations in binarycollection.

So given the example:

binary:
1
2
3
4
5
6
7

binarycollection:
(binaryid    collectionid)
1   1
2   1
3   1
3   2
4   1
4   2
5   2
6   2

It should return binaryids 1, 2, 5, and 6.

Any help is appreciated. 🙂

ps. This needs to be efficient, the tables contain millions of rows.

Answer 1

Use GROUP BY :

Select binaryid from binarycollection group by binaryid having count(*)=1