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From:John Bonnett Date:March 17 2009 10:59pm
Subject:RE: Negated SELECT query
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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:bobsharp@stripped] 
Sent: Wednesday, 18 March 2009 3:13 AM
To: mysql@stripped
Cc: win32@stripped; mysql-help@stripped
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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Thread
Negated SELECT queryBobSharp17 Mar
  • Re: Negated SELECT queryPerrin Harkins17 Mar
  • RE: Negated SELECT queryJohn Bonnett17 Mar
  • Re: Negated SELECT queryBobSharp18 Mar