Query to determine percentage composition on a specific grouping of records I want to analyse the Market capital of the Industry per Counterparty of the following table:

--------------------------------------------------
| CPTY | Industry      | Value   |
--------------------------------------------------
| a    | food          | 10      |
| a    | water         | 5       |
| c    | wood          | 20      |
| c    | food          | 20      |
| d    | wood          | 10      |


I would like a breakdown of percentages for each of the CPTY fields in relation to their child Industries.

A sample of the output query I would expect should look like:



| CPTY | Industry      | Value   | %IndustryPerCpty
--------------------------------------------------
| a    | food          | 10      | 66.66
| a    | water         | 5       | 33.33
| c    | wood          | 20      | 50.0
| c    | food          | 20      | 50.0
| d    | wood          | 10      | 100.00


E.g. for CPTY a, the corresponding sectors are food and water. The total value for CPTY a is 10+5=15. Thus, food has 10/15*100% = 66.66% of the total market value for that CPTY. Likewise, water has 5/15 *100% = 33.33% of the total market value for that CPTY.

My original attempts at the query follow the structure adopted in accepted answer here. However, this gives me percentage composition for each row, not the Industry per CPTY. 

Note: I don't expect the sum( %IndustryPerCpty ) column to equal 100%, for reasons I hope are clear.

Can anyone suggest a query structure in Ms Access to generate my desired table with %IndustryPerCpty fields?
Assuming your table is called [t], and that the Value column has been called Val (Value is a reserved word and complicates things), you can create a view (query) with the following SQL definition:

SELECT 
    t0.CPTY, t0.Industry, t0.Val * 100.0 / 
    (SELECT sum(t1.Val) FROM t AS t1    
      WHERE t1.CPTY = t0.CPTY) AS PerCentIndustryPerCpty
FROM 
    t AS t0;


You can make it using the "SQL view" instead of the graphical designer for views (querys).

You get this result:





If you don't feel comfortable with the SQL view, this can also be done within the GUI, in two steps:


Create a Query named TotalsPerCPTY with a column named TotalValPerCPTY that has the SUMs of Val GROUPed BY CPTY, as shown in the following image:





Create the ViePerCents Query by joining the t table together with the TotalsPerCPTY view, using the CPTY column, with one computed column that computes Val / TotalValPerCPTY * 100.0: