Query to determine percentage composition on a specific grouping of records
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: