Two Tables with Left Outer Join & Where Clause

[pbassutti]

Hello,

I'm trying to link two tables... one for Employees and the other for
Timecards

I need to get a list of employees that do not have timecards on an
SPECIFIC DATE

I tried the follonwing

SELECT Employess.EmployeeID
FROM Employees LEFT OUTER JOIN Timecards on Employees.EmployeeID =
Timecards.lmpEmployeeID
WHERE lmpEmployeeID is NULL and lmpTimecardDate = '10/24/2007'

But it doesn't work. However, when I comment the date condition out
(lmpTimecardDate = '10/24/2007') it works all right but It's not what
I need

Another interesting point... if I use the following query... it works
all right

SELECT Employess.EmployeeID
FROM Employees
WHERE Employees.EmployeeID not in (select Timecards.EmployeeID from
Timecards
where TimecardDate = '10/24/2007')

I'd like to be able to use the Left Outer Join option.... Am I doing
something wrong?... or is it that if It doesn't like the condition I'm
usgin in the WHERE clause (TimecardDate = '10/24/2007')

Thanks for your help

Pablo

[David Portas]

<pb*******@hotmail.comwrote in message
news:11**********************@i13g2000prf.googlegr oups.com...

Hello,

I'm trying to link two tables... one for Employees and the other for
Timecards

I need to get a list of employees that do not have timecards on an
SPECIFIC DATE

I tried the follonwing

SELECT Employess.EmployeeID
FROM Employees LEFT OUTER JOIN Timecards on Employees.EmployeeID =
Timecards.lmpEmployeeID
WHERE lmpEmployeeID is NULL and lmpTimecardDate = '10/24/2007'

But it doesn't work. However, when I comment the date condition out
(lmpTimecardDate = '10/24/2007') it works all right but It's not what
I need

Another interesting point... if I use the following query... it works
all right

SELECT Employess.EmployeeID
FROM Employees
WHERE Employees.EmployeeID not in (select Timecards.EmployeeID from
Timecards
where TimecardDate = '10/24/2007')

I'd like to be able to use the Left Outer Join option.... Am I doing
something wrong?... or is it that if It doesn't like the condition I'm
usgin in the WHERE clause (TimecardDate = '10/24/2007')

Thanks for your help

Pablo

Put any outer (non-preserved) table references into the ON clause:

SELECT Employess.EmployeeID
FROM Employees
LEFT OUTER JOIN Timecards
ON Employees.EmployeeID = Timecards.lmpEmployeeID
AND lmpTimecardDate = '20071024'
WHERE lmpEmployeeID is NULL ;

--
David Portas

[Erland Sommarskog]

(pb*******@hotmail.com) writes:

SELECT Employess.EmployeeID
FROM Employees LEFT OUTER JOIN Timecards on Employees.EmployeeID =
Timecards.lmpEmployeeID
WHERE lmpEmployeeID is NULL and lmpTimecardDate = '10/24/2007'

But it doesn't work. However, when I comment the date condition out
(lmpTimecardDate = '10/24/2007') it works all right but It's not what

In addition to David's post, here is what is happening:

The FROM ... LEFT JOIN operators define a table that includes all rows
in the outer table, Employees in this case. This table includes the columns
from the Timecards table, but for the employees there there is no timecard,
all columns have NULL. Which you apparently have understood, since you
the condition "lmpEmployeeID IS NULL". But then there is a lapse, and you
filter lmpTimecardDate despite it is not likely that there is a row in
Timecards where the date is non-NULL and the employee ID is NULL. (At least
one would hope so!) Moving the date condition to the ON clause addresses
the issue, as it now will be part of the condition that builds the
table that is then filtered by WHERE.

Personally, I would prefer to write this query with NOT EXISTS:

SELECT E.Employee
FROM Employees E
WHERE NOT EXISTS (SELECT *
FROM Timecards T
WHERE E.EmployeeID = T.lmpEmployeeID
AND T.lmpTimecardDate = '20071014')

Simply because this clearly express what this is all about.

And I would also use a date format that is safe from misinterpretations.
--
Erland Sommarskog, SQL Server MVP, es****@sommarskog.se

Books Online for SQL Server 2005 at
http://www.microsoft.com/technet/pro...ads/books.mspx
Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodinf...ons/books.mspx

[pbassutti]

On Oct 30, 9:22 am, Erland Sommarskog <[e-mail]:

([e-mail]) writes:

SELECT Employess.EmployeeID
FROM Employees LEFT OUTER JOIN Timecards on Employees.EmployeeID =
Timecards.lmpEmployeeID
WHERE lmpEmployeeID is NULL and lmpTimecardDate = '10/24/2007'

But it doesn't work. However, when I comment the date condition out
(lmpTimecardDate = '10/24/2007') it works all right but It's not what

In addition to David's post, here is what is happening:

The FROM ... LEFT JOIN operators define a table that includes all rows
in the outer table, Employees in this case. This table includes the columns
from the Timecards table, but for the employees there there is no timecard,
all columns have NULL. Which you apparently have understood, since you
the condition "lmpEmployeeID IS NULL". But then there is a lapse, and you
filter lmpTimecardDate despite it is not likely that there is a row in
Timecards where the date is non-NULL and the employee ID is NULL. (At least
one would hope so!) Moving the date condition to the ON clause addresses
the issue, as it now will be part of the condition that builds the
table that is then filtered by WHERE.

Personally, I would prefer to write this query with NOT EXISTS:

SELECT E.Employee
FROM Employees E
WHERE NOT EXISTS (SELECT *
FROM Timecards T
WHERE E.EmployeeID = T.lmpEmployeeID
AND T.lmpTimecardDate = '20071014')

Simply because this clearly express what this is all about.

And I would also use a date format that is safe from misinterpretations.

--
Erland Sommarskog, SQL Server MVP, [e-mail]

Books Online for SQL Server 2005 athttp://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books...
Books Online for SQL Server 2000 athttp://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

Thanks a lot guys...

That worked perfectly... and thanks for the explanation and
suggestions

Regards

Pablo