Choose between two different date ranges - sql

Question

I have a check box, when checked, my date range flips causing me now to choose which date range to look at.
So, 4/15/14 thru 4/20/14 … when my check box is checked, this date range is now 4/10/14 thru 4/15/14.
In my SQL Select I need to chose, based on this check box, which date range.
This didn't work ??
Where ( ? Between Date_1 and Date_2 ) or ( ? Between Date_2 and Date_1 )
Nor did this work ??
Where ( ?
Case
When Ck_Bx Is Null
Then Date_2 and Date_1
Else Date_1 and Date_2
End
)
Here is the SQL THAT IS WORKING AND I AM TRYING TO MODIFY THE "WHERE CLAUSE"
ExecuteSQL ( "
Select ToDo_Name_Calc, ToDo_Name
From ToDo
WHERE ( ( ? Between ToDo_Alert_Date and ToDo_Date ) or ( ? Between ToDo_Date and ToDo_Alert_Date ) ) and ToDo_Ck_Bx Is Null
Order By ToDo_Alert_Date Asc " ; " - " ; "" ;
cDateOfFirstPortal +11 )
Any assistance I would be grateful.
Tom

Answer 1

between is really just a syntax shortcut and it is the exact equivalent of:
( field >= small-value and field <= larger-value )
Let's say we use 2014-04-20 as the larger-value, but the field contains time as well as date. So evaluating <= 2014-04-20 against a stored value of 2014-04-20 11:12:13 means that value is ignored. In truth we really do want that value included (it occurs DURING the day of 2014-04-20) and the most reliable way of protecting we don't make that mistake is to get all data that is less than 2014-04-21.
So, the greatest problem faced when using date ranges using between is that you could miss almost 24 hours of data if you get it wrong. A safer approach avoids this problem by using less than for the upper date - but you add one day to it, and because we need to add one day we may have to use database specific code (e.g. date_add() for MySQL, dateadd() for SQL Server/Sybase).
Not using between, which is the safer option, requires some date arithmetic, represent here simply by +1
SELECT
ToDo_Name_Calc
, ToDo_Name
FROM ToDo
WHERE (
? >= ToDo_Alert_Date AND ? < (ToDo_Date+1) --*
AND ToDo_Ck_Bx IS NULL)
OR (
? >= ToDo_Date AND ? < (ToDo_Alert_Date+1) --*
AND ToDo_Ck_Bx IS NOT NULL
)
ORDER BY
ToDo_Alert_Date ASC
--* use the relevant date addition method for your dbms.
Another reason for not using between here is that the dates MUST be in a specific order or nothing is returned', the older date must be first, the younger date must be last. You cannot just reverse them inside the between syntax.