Access 2007 embedded Iif statement - ms-access

Question

Using Access 2007
My table has 9 columns. I have 4 columns I need to use to select a value based on dates in 3 other columns. In a nutshell, I need the most current cost to show in the last column (Current_Cost). I have tried several embedded Iif statements to no avail. I don’t know if I have been looking at this too long and I’m just not seeing my error or if I’m way off base.
Columns in table:
Item Number
Original Cost
Original Date
Cost 1
Date 1
Cost 2
Date 2
Cost 3
Date 3
UPDATE MyTable
SET Current_Cost =
IIf([MyTable]![DATE3]>[MyTable]![DATE 2],[MyTable]![COST 3],
IIf([MyTable]![DATE2]>[MyTable]![DATE 1],[MyTable]![COST 2],
IIf([MyTable]![DATE1]>[MyTable]![ORIGINAL DATE],[MyTable]![COST 1],
[MyTable]![ORIGINAL COST])));
FYI - I inherited this table so please don't bash me for the way it is set up!

Answer 1

I think Switch is easier to manage than a bunch of nested IIf expressions.
First try a SELECT query to work out the Switch logic. I think this is close to what you're aiming for:
SELECT
Switch
(
[DATE 3]>[DATE 2], [COST 3],
[DATE 2]>[DATE 1], [COST 2],
[DATE 1]>[ORIGINAL DATE], [COST 1],
True, [ORIGINAL COST]
) AS test_expression,
*
FROM MyTable;
After you have the correct Switch expression, you can use that in your UPDATE.
UDATE MyTable
SET Current_Cost =
Switch
(
[DATE 3]>[DATE 2], [COST 3],
[DATE 2]>[DATE 1], [COST 2],
[DATE 1]>[ORIGINAL DATE], [COST 1],
True, [ORIGINAL COST]
)

Answer 2

Interesting question, because of the multiple dates. First off: can you guarantee that the following statement always holds true for your table:
[ORIGINAL DATE] <= [DATE1] <= [DATE2] <= [DATE3]
If it does, your query will be a simple switch statement as per #HansUp's answer.* If it doesn't, then things become a little more interesting. My approach would be (and note that this will only work within the same Access database file as the query) to define a VBA function that takes two values and returns their maximum, let's call it Max2, then use this function to find the latest date for each row in the table, then pick the cost corresponding to that date:
update MyTable
set Current_Cost = switch(
DATE3 = Max2(Max2(Max2([ORIGINAL DATE], DATE1), DATE2), DATE3), [COST 3]
, DATE2 = Max2(Max2(Max2([ORIGINAL DATE], DATE1), DATE2), DATE3), [COST 2]
, DATE1 = Max2(Max2(Max2([ORIGINAL DATE], DATE1), DATE2), DATE3), [COST 1]
, true, [ORIGINAL COST]
)
The Max2 VBA function (can be defined in any module):
public sub Max2(v1 as variant, v2 as variant) as variant
if v1 < v2 then
Max2 = v2
else
Max2 = v1
end if
end sub
By the way, why Max2 and not just Max4? Reusability. You can use a function like this in many different places.
* You can check with a simple SQL query. You can also enforce this date order as a table check constraint in Access. Let me know if you need more info.

Answer 3

Let's evaluate what an IIF does:
IIF(SOME_CHECK,true_condition,false_condition)
Looking at your code, we see:
If
[MyTable]![DATE3]>[MyTable]![DATE 2]
then set Current_cost to be:
[MyTable]![COST 3]
Else go on to the next check..
If
[MyTable]![DATE2]>[MyTable]![DATE 1]
then set Current_cost to be:
[MyTable]![COST 2]
Else go on to the next check..
If
[MyTable]![DATE1]>[MyTable]![ORIGINAL DATE]
then set Current_cost to be:
[MyTable]![COST 1]
Else set to
[MyTable]![ORIGINAL COST]
So, is that what you are looking for?
If it is not, you may need to reverse your logic.. Instead of Cost 3, Cost 2, Cost 1 then change to Cost 1, Cost 2, and Cost 3..