Question

I’m facing a weird issue and I can’t understand what’s wrong.
In my database I have a datetime field, which keeps some values like: 03.10.2012 11:25:06
I need to convert it to date and compare it with another date. What I have tried without success is:

p1.value as City,
p2.value as Country,
p3.value as RequestNumber,
convert (datetime, convert (varchar, test.timestampmin, 101), 101) as timestampmin

from Process p
LEFT JOIN Parameter p1 on p1.ID=p.id AND p1.NAME = 'City'
LEFT JOIN Parameter p2 on p2.ID=p.id AND p2.NAME = 'Country'
LEFT JOIN PA_Parameter p3 on p3.ID=p.id AND p3.NAME = 'RequestNumber'

INNER JOIN
(
    SELECT min(Timestamp) as timestampmin, id as id
    FROM tasks
    GROUP BY id
) as test 
    ON test.id = p3.ID

where p.type='Event' and 
timestampmin = convert (datetime, convert (varchar, '06.18.2012', 101), 101)

The problem is that I can’t compare the converted datetime with the convert (datetime, convert (varchar, '06.18.2012', 101), 101) which I’m using in the where clause.

What am I missing?

Answer 1

Quite simply, you cannot access column aliases in the SELECT clause within the WHERE clause of the same query.

p1.value as City,
p2.value as Country,
p3.value as RequestNumber,
convert (datetime, convert (varchar, test.timestampmin, 101), 101) as timestampmin

from Process p
LEFT JOIN Parameter p1 on p1.ID=p.id AND p1.NAME = 'City'
LEFT JOIN Parameter p2 on p2.ID=p.id AND p2.NAME = 'Country'
LEFT JOIN PA_Parameter p3 on p3.ID=p.id AND p3.NAME = 'RequestNumber'

INNER JOIN
(
    SELECT min(Timestamp) as timestampmin, id as id
    FROM tasks
    GROUP BY id
) as test 
    ON test.id = p3.ID

where p.type='Event' and 
convert (datetime, convert (varchar, test.timestampmin, 101), 101)
   = convert (datetime, convert (varchar, '06.18.2012', 101), 101)

And if test.timestampmin is a datetime column, you can use this in the WHERE clause instead

where p.type='Event'
  and test.timestampmin >= '20120618'
  and test.timestampmin <  '20120619'