I am trying to improve query readability by using a function in SQL Server

Question

0

Asked: May 25, 20262026-05-25T23:09:20+00:00 2026-05-25T23:09:20+00:00

I am trying to improve query readability by using a function in SQL Server

0

I am trying to improve query readability by using a function in SQL Server Express 2008.
Here is a sample of what I’m trying to do.

I have a table where we store a max temperatures reading per hour of the day, then I want to select all days where the max temperature between 8-10AM was greater than the max temp between 12-2PM

So here is how it’s like:

DECLARE @TableA TABLE ([Date] DATE, [Time] TIME(0), HighTemp DECIMAL(6,2)); 

INSERT @TableA VALUES 
('2011-09-10','08:00:00',38.15), 
('2011-09-10','09:00:00',38.32), 
('2011-09-10','10:00:00',38.17), 
('2011-09-10','11:00:00',38.10), 
('2011-09-10','12:00:00',38.05), 
('2011-09-10','13:00:00',38.15), 
('2011-09-10','14:00:00',38.30), 

('2011-09-11','08:00:00',38.12), 
('2011-09-11','09:00:00',38.09), 
('2011-09-11','10:00:00',38.07), 
('2011-09-11','11:00:00',38.15), 
('2011-09-11','12:00:00',38.13), 
('2011-09-11','13:00:00',38.11), 
('2011-09-11','14:00:00',38.10), 

('2011-09-12','08:00:00',38.30), 
('2011-09-12','09:00:00',38.33), 
('2011-09-12','10:00:00',38.35), 
('2011-09-12','11:00:00',38.30), 
('2011-09-12','12:00:00',38.25), 
('2011-09-12','13:00:00',38.23), 
('2011-09-12','14:00:00',38.20)

select distinct [DATE] from @TableA maintbl
where 
-- Select the high temp between 08:00:00-10:00:00
(select MAX(HighTemp) from @TableA tmptbl where tmptbl.Time >= '08:00:00' and tmptbl.Time <= '10:00:00' and maintbl.Date = tmptbl.Date)
>
-- Select the high between 12:00:00-14:00:00
(select MAX(HighTemp) from @TableA tmptbl where tmptbl.Time >= '12:00:00' and tmptbl.Time <= '14:00:00' and maintbl.Date = tmptbl.Date)

The query runs well (fast) and the result for the above query should be:
2011-09-10
2011-09-12

Now, I have tried to simplify the query by using a function that retrieves the max tempreture in a certain day and time period, so the query is easier to read, like so:

select distinct [DATE] from @TableA maintbl
where GetPeriodHigh(maintbl.Date, '08:00:00', '10:00:00') > GetPeriodHigh(maintbl.Date, '12:00:00', '14:00:00')

And the function is like so:

CREATE FUNCTION [dbo].[GetPeriodHigh] 
(
    @Date date,
    @From time,
    @To time
)
RETURNS decimal(6,2)
AS
BEGIN

    declare @res decimal(6,2)

    select @res = MAX(high) from MyTable
    where Time >= @from and Time <= @to and Date = @Date

    return @res
END

The problem is that running the query using the function takes LOOONG time, actually I never saw it finishes, looks like it is in some sort of infinite loop…

Any ideas why is that, and there is anything I can do to simplify my query?

Thx.