Calculate Weekly Usage

I have a table, updated weekly since the beginning of the year, which contains the fields Equipment_ID, FiscalWeek and Gas_Level. I need a query that will calculate the weekly usage, by Equipment ID, for each site.

I am close but, when I run the query, I get a popup asking me to enter Prior and Current Readings. If I just click enter it runs fine but I would like to get rid of the popup.

SELECT tbl_YTD_Weekly_Readings.[Equipment_ID], "2" AS FiscalWeek, Format([Prior_Gas]-[Current_Gas],"00.0") AS Weekly_Usage, Sum(IIf([tbl_YTD_Weekly_Readings].[FW]=122,[tbl_YTD_Weekly_Readings].[He Level],0)) AS Current_Gas, Sum(IIf([tbl_YTD_Weekly_Readings].[FW]=121,[tbl_YTD_Weekly_Readings].[He Level],0)) AS Prior_Gas
FROM tbl_YTD_Weekly_Readings
GROUP BY tbl_YTD_Weekly_Readings.[Equipment_ID], "2", Format([Prior_Gas]-[Current_Gas],"00.0");

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Jeffrey CoachmanMIS LiasonCommented:
Not sure without a sample dB to examine...

Basically a Parameter prompt will occur when Access does not recognize the field or control.
...Or the Field/Control is not available when the code is run.
(The form that supplies these values is closed0

So obviously "Prior and Current Readings" fall under one of these scenarios.
So start there with your troubleshooting

You are using this values as field names (... AS Current_Gas). In this case add table name to your original fields:
JazCatAuthor Commented:
als315, the Prior and Current Gas values are calculated within the same query. For example, Current_Gas is the reading if, in the sample snippet, the Fiscal Week = 122. 122, in case anyone cares, is just the way the database assigns for Year 12 FiscalWeek 2.

Jeff, could that be because the Current and Prior Readings are calculated? Would it be better to create the Calculated fields in one query then, using that query, create the differences field?  I can do that.
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Jeffrey CoachmanMIS LiasonCommented:
<Jeff, could that be because the Current and Prior Readings are calculated? Would it be better to create the Calculated fields in one query then, using that query, create the differences field?>
Again, not sure with no sample DB to examine...

Expert als315 is phenomenal at these types of questions.
To avoid confusion, I will let you continue on with him.

HainKurtSr. System AnalystCommented:
try this

SELECT [Equipment_ID], "2" AS FiscalWeek, Format([Prior_Gas]-[Current_Gas],"00.0") AS Weekly_Usage, Sum(IIf([FW]=122,[He Level],0)) AS Sum_Current_Gas, Sum(IIf([FW]=121,[He Level],0)) AS Sum_Prior_Gas
FROM tbl_YTD_Weekly_Readings
GROUP BY [Equipment_ID], "2", Format([Prior_Gas]-[Current_Gas],"00.0");

do not use same alias for your columns, I prefixed them with "sum_"
@Jeff: Two heads is always better then one :)

@ JazCat:
Your question (could that be because the Current and Prior Readings are calculated?) is absolutely correct. There are two possible solutions:
1. Do any calculations with these values in next query
2. Don't use calculated field in same query, use source data (you will not be able to use format function in this case):
SELECT tbl_YTD_Weekly_Readings.[Equipment_ID], "2" AS FiscalWeek, Sum(IIf([tbl_YTD_Weekly_Readings].[FW]=121,[tbl_YTD_Weekly_Readings].[He Level],0)-IIf([tbl_YTD_Weekly_Readings].[FW]=122,[tbl_YTD_Weekly_Readings].[He Level],0)) AS Weekly_Usage 
FROM tbl_YTD_Weekly_Readings
GROUP BY tbl_YTD_Weekly_Readings.[Equipment_ID], "2";

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I can agree with Jeff - sample database is very helpful
JazCatAuthor Commented:
Sorry, got pulled off onto another more urgent project. Will see if I can post a sample database tomorrow.
JazCatAuthor Commented:
I apologize, totally forgot this was open. What I ended up doing was creating two tables, tbl_prior_readings and tbl_current_readings, with exactly the same data. Then I used them in a query where I set the criteria for the tbl_prior_reading![prior_FW] to tbl_current_readings![current_FW]-1. That worked and let me make my calculations with no problems.

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JazCatAuthor Commented:
I tried the other suggestions but they didn't work totally. Reading them did give me more ideas which ultimately ended up fixing the problem.
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