Thanks for that, worked through and found that this gives the correct
result ...
--- Employee No Assets ---
SELECT DISTINCT e.employeeID AS eID,
concat(e.firstname, " ", e.lastname) AS eName
FROM employees e LEFT JOIN assets a ON e.employeeID = a.employeeID
WHERE e.employeeID IS NULL
ORDER BY e.employeeID
--- Employee No History ---
SELECT DISTINCT a.assetID AS aCode,
LEFT(a.assetdescription,60) AS aTitle,
c.assetcategory AS cCategory
FROM assets a LEFT JOIN maintenance m ON m.assetID = a.assetID
LEFT JOIN assetcategories c ON a.assetcategoryID = c.assetcategoryID
WHERE m.assetID IS NULL
ORDER BY a.assetID
Cheers
----- Original Message -----
From: "Bonnett, John" <john.bonn...@vision.zeiss.com>
To: <bobsh...@ntlworld.com>; <mysql@lists.mysql.com>
Cc: <wi...@lists.mysql.com>; <mysql-h...@lists.mysql.com>
Sent: Tuesday, March 17, 2009 10:59 PM
Subject: RE: Negated SELECT query
SELECT Employees.*
FROM Employees LEFT JOIN Assets ON Employess.EmployeeID =
Assets.EmployeeID
WHERE Assets.EmployeeID IS NULL
The one for assets with no maintenance is similar. The point is the left
join above produces in its output all rows from the Employees table
regardless of whether anything matches in the assets table. By selecting
only rows where the foreign key field in the assets table is null gives
you the employees having no assets.
John Bonnett
-----Original Message-----
From: BobSharp [mailto:bobsh...@ntlworld.com]
Sent: Wednesday, 18 March 2009 3:13 AM
To: mysql@lists.mysql.com
Cc: wi...@lists.mysql.com; mysql-h...@lists.mysql.com
Subject: Negated SELECT query
3 tables are related by one-many links.
Employees ---<- Assets ---<- Maintenance
Employees can be assigned => 0 Assets
Assets can have => 0 occurances of Maintenance.
Assets table contains EmployeeIDs and MaintenanceIDs, but no Foreign
Key contraints.
Queries ...
1) which Employees do not have any Assets ?
2) which Assets have not had any Maintenance ?
These have been written successfully with Sub-Queries,
I would like to know how they can be done with only JOINs ?
(that also means without the EXCEPT statement)
Is that too much of a challenge ? (MySQL 5.0.67)
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