Question : Need help understranding 'WHERE EXISTS' and 'WHERE NOT EXISTS'

Hi all

Finally have come up against an SQL command that I can;t seem to make work. I'm sure it's just that I am thick, but I really want to know how this works as I can see it being quite useful in a number of instances... here's the example:

I have two tables. One is a list of services. The other is a list of services used by each client. I want to build a list of services NOT already assigned to a client. I was using the following command:

SELECT serviceid
FROM services
WHERE NOT EXISTS (
SELECT serviceid
FROM insp_client_services
WHERE clientid=2 )

The services table has the follwoing data:

(`serviceid`, `description`)
(1, '10% (outside area 2)'),
(3, 'Digital photos'),
(101, 'new service for test');

The clientservices table has the following data:

(`clientserviceid`, `serviceid`, `clientid`)
(727, 1, 2),
(729, 3, 2),
(910, 1, 3),
(912, 3, 3);

What I would expect from the above is one record for serviceid 101 to be the result. The result I get is empty. I know this one will be humbling, but can anyone see where I have gone wrong? I definitely have been staring at it too long to see something that is most assuredly quite obvious...

TIA
Owen

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             CREATE TABLE IF NOT EXISTS `services` (
  `serviceid` int(11) NOT NULL auto_increment,
  `description` varchar(50) NOT NULL,
  PRIMARY KEY  (`serviceid`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=102 ;
 
-- 
-- Dumping data for table `services`
-- 
 
INSERT INTO `services` (`serviceid`, `description`) VALUES 
(1, '10% (outside area 2)'),
(3, 'Digital photos');
 
-- 
-- Table structure for table `clientservices`
-- 
 
CREATE TABLE IF NOT EXISTS `clientservices` (
  `clientserviceid` int(11) NOT NULL auto_increment,
  `serviceid` int(11) NOT NULL default '0',
  `clientid` int(11) NOT NULL default '0',
  PRIMARY KEY  (`clientserviceid`),
  KEY `services_list` (`clientid`,`serviceid`,`clientserviceid`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=971 ;
 
-- 
-- Dumping data for table `clientservices`
-- 
 
INSERT INTO `clientservices` (`clientserviceid`, `serviceid`, `clientid`) VALUES 
(727, 1, 2),
(729, 3, 2),
(910, 1, 3),
(912, 3, 3);

           
         

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Answer : Need help understranding 'WHERE EXISTS' and 'WHERE NOT EXISTS'

hi,

SELECT serviceid
FROM services
WHERE NOT EXISTS (
SELECT serviceid
FROM insp_client_services
WHERE clientid=2 and services.serviceid = insp_client_services.serviceid )

Question : Need help understranding 'WHERE EXISTS' and 'WHERE NOT EXISTS'

Answer : Need help understranding 'WHERE EXISTS' and 'WHERE NOT EXISTS'

hi,SELECT serviceid FROM services WHERE NOT EXISTS ( SELECT serviceid FROM insp_client_services WHERE clientid=2 and services.serviceid = insp_client_services.serviceid )

hi,

SELECT serviceid
FROM services
WHERE NOT EXISTS (
SELECT serviceid
FROM insp_client_services
WHERE clientid=2 and services.serviceid = insp_client_services.serviceid )