The query in question that does not work is this one: SELECT Credits.BillingPeriod, Sum(Credits.Credit) AS SumOfCredit I want these queries to be flexible enough that it will display a summary with or without a particular charge/credit, because you might not be charged for it one month, and you may be charged for it during another month. That is all fine and dandy, but the problem arises when the Item Code is not found. For example, one query I have working that sums ancillary charges for all billing months would be SELECT Charges.BillingPeriod, Sum(Charges.Charge) as SumOfCharge To create this report I group the charges and credits and sum them based on the item codes I have. The Charge Table and Credit Table look basically the same, with only one field being different, as shown below BillingPeriod | ItemCode | ItemName | Charge(Credit) | IsAdjustment | AdjustmentDate | ReportTimestamp

I am trying to create a report of charges and credits based on a table of Charges and Credits that are parsed from a CSV file.

Thorium charges item code