Coalesce Question

Hi.
I'm using Coalesce to change a NULL returned value from a Select statement.
Here's my code:
SELECT TOP 1 @.StartDate = Coalesce(Discount_Effect_Date, '01/01/1980') FROM
MyTable WHERE RTrim(Subtable_Id) = 'I03U'
Print @.StartDate
When I have a row in MyTable where the Subtable_Id = 'I03U' I get the
@.StartDate
printed out.
When I don't have a row in MyTable where the Subtable_Id = 'I03U' I don't
get the @.StartDate printed out. I was expecting to see 01/01/1980.
What am I missing?
TIA.
RitaRitaG wrote:
> Hi.
> I'm using Coalesce to change a NULL returned value from a Select statement
.
> Here's my code:
> SELECT TOP 1 @.StartDate = Coalesce(Discount_Effect_Date, '01/01/1980') FRO
M
> MyTable WHERE RTrim(Subtable_Id) = 'I03U'
> Print @.StartDate
> When I have a row in MyTable where the Subtable_Id = 'I03U' I get the
> @.StartDate
> printed out.
> When I don't have a row in MyTable where the Subtable_Id = 'I03U' I don't
> get the @.StartDate printed out. I was expecting to see 01/01/1980.
> What am I missing?
> TIA.
> Rita
The problem is that if the SELECT doesn't return any rows then the
assignment will never be made. For single value assignments use SET
instead of SELECT.
SET @.startdate =
(SELECT COALESCE(MIN(discount_effect_date),'1980
0101')
FROM mytable
WHERE RTRIM(subtable_id) = 'I03U');
I assume you meant to retrieve the minimum date but in the query you
posted you specified TOP without ORDER BY so in fact your results may
be unpredictable.
The YYYYMMDD format I've used is better for dates because it's
unambiguous and doesn't depend on any of your regional connection
settings.
Hope this helps.
David Portas, SQL Server MVP
Whenever possible please post enough code to reproduce your problem.
Including CREATE TABLE and INSERT statements usually helps.
State what version of SQL Server you are using and specify the content
of any error messages.
SQL Server Books Online:
http://msdn2.microsoft.com/library/ms130214(en-US,SQL.90).aspx
--|||Coalesce works on individual columns, for each row returned by your query.
If no row is returned, then there is no column value for coalesce to work
on. Coalesce is only useful when you have rows returned, but a particular
column is null, and you want to return a default value instead of the null.
You need to either change your SQL to insure that a row is always returned
(probably not what you want to do) or check to see if any rows were returned
(which appears to be your goal anyway).
Simply checking to see if @.StartDate is null AFTER your select may
accomplish what you want.
If you post the rest of your code, folks may be able to give some better
advice. Since this code is out of context, I can only guess at what you are
doing with it.
"RitaG" <RitaG@.discussions.microsoft.com> wrote in message
news:F739466D-0D03-4843-A46B-E9F3BF0AD5AB@.microsoft.com...
> Hi.
> I'm using Coalesce to change a NULL returned value from a Select
statement.
> Here's my code:
> SELECT TOP 1 @.StartDate = Coalesce(Discount_Effect_Date, '01/01/1980')
FROM
> MyTable WHERE RTrim(Subtable_Id) = 'I03U'
> Print @.StartDate
> When I have a row in MyTable where the Subtable_Id = 'I03U' I get the
> @.StartDate
> printed out.
> When I don't have a row in MyTable where the Subtable_Id = 'I03U' I don't
> get the @.StartDate printed out. I was expecting to see 01/01/1980.
> What am I missing?
> TIA.
> Rita|||"RitaG" <RitaG@.discussions.microsoft.com> wrote in message
news:F739466D-0D03-4843-A46B-E9F3BF0AD5AB@.microsoft.com...
> Hi.
> I'm using Coalesce to change a NULL returned value from a Select
> statement.
> Here's my code:
> SELECT TOP 1 @.StartDate = Coalesce(Discount_Effect_Date, '01/01/1980')
> FROM
> MyTable WHERE RTrim(Subtable_Id) = 'I03U'
> Print @.StartDate
> When I have a row in MyTable where the Subtable_Id = 'I03U' I get the
> @.StartDate
> printed out.
> When I don't have a row in MyTable where the Subtable_Id = 'I03U' I don't
> get the @.StartDate printed out. I was expecting to see 01/01/1980.
> What am I missing?
> TIA.
> Rita
Your WHERE clause only allows data to be printed out WHERE your Subtable ID
= I03U.
The other issue I see here is the use of your COALESCE... While this should
work for what you are doing, an ISNULL(Discount_Effect_Date, '01/01/1980')
may work better for you. COALESCE is generally used to find the first
non-null value in a list of columns. For example COALESCE(payrate_salary,
payrate_daily, payrate_hourly)
Rick Sawtell
MCT, MCSD, MCDBA|||Thanks to all for your responses.
The dates are all the same that satisfy the WHERE clause so I could have
used a Distinct but I think Top 1 is faster.
The SET @.startdate =
(SELECT COALESCE(MIN(discount_effect_date),'1980
0101')
FROM mytable
WHERE RTRIM(subtable_id) = 'I03U');
will work for me. Thanks for the "YYYYMMDD format" suggestion.
Learn something every day! :-)
"David Portas" wrote:

> RitaG wrote:
> The problem is that if the SELECT doesn't return any rows then the
> assignment will never be made. For single value assignments use SET
> instead of SELECT.
> SET @.startdate =
> (SELECT COALESCE(MIN(discount_effect_date),'1980
0101')
> FROM mytable
> WHERE RTRIM(subtable_id) = 'I03U');
> I assume you meant to retrieve the minimum date but in the query you
> posted you specified TOP without ORDER BY so in fact your results may
> be unpredictable.
> The YYYYMMDD format I've used is better for dates because it's
> unambiguous and doesn't depend on any of your regional connection
> settings.
> Hope this helps.
> --
> David Portas, SQL Server MVP
> Whenever possible please post enough code to reproduce your problem.
> Including CREATE TABLE and INSERT statements usually helps.
> State what version of SQL Server you are using and specify the content
> of any error messages.
> SQL Server Books Online:
> http://msdn2.microsoft.com/library/ms130214(en-US,SQL.90).aspx
> --
>