My queries are running so slowly!

Thanks for that!

OK, i think I understand what this is doing. I've put this into the function fxSecRunningTotal and now adjusting the made bit of code.

Additional question though, I need to do this for three different fields. At the moment I have the same function three times, but with different names (the running totals are calculated in different queries, of which I've shared the code for just one). Am I right in thinking I can remove the other two functions, and just use this new one?

It's defintiely running faster (thank you!!), but now I'm getting a couple of errors and I can't figure out how to fix them.

1. It's saying the column 'Sec Total Avg SEI' wasn't found. It's in the source table, and if I was to manually expand the columns, it's in the expandable columns too. Do I need to expand all the columns that I need?

2. The running total column just errors. I think I may have the wrong field selected within the code!

fxSecRunningTotal
let
func = (Table as table, SortColumn as text, AmountColumn as text) =>

let
/* Debug parameters
Table = #"4c - Sec Data Table", 
SortColumn = "CaseNo", 
AmountColumn = "Sec Avg Activity SEI",
*/

// Sort table and buffer it
    Sorted = Table.Buffer(Table.AddIndexColumn(Table.Sort(Table,{{SortColumn, Order.Ascending}}), "Index",1,1)),
// Select the Columns
    SelectColumns = Table.SelectColumns(Sorted, {SortColumn, AmountColumn, "Index"}),
// Extract Amount column and buffer it
    ExtractAmountColumn = List.Buffer(Table.Column(SelectColumns, AmountColumn)),
// Calculate a list with all running Totals
    RunningTotal = List.Skip(List.Generate( ()=> [ListItem=0, Counter=0]
                                            ,each [Counter] <= List.Count(ExtractAmountColumn)
                                            ,each [ ListItem = ExtractAmountColumn{[Counter]}+[ListItem],
                                                    Counter = [Counter]+1
                                                   ]
                                            ),1),
    ConvertedTable = Table.FromList(RunningTotal, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    ExpandedColumn = Table.ExpandRecordColumn( ConvertedTable, "Column1", {"ListItem", "Counter"}, {"ListItem", "Counter"}),
    MergedQueries = Table.NestedJoin(Sorted,{"Index"}, ExpandedColumn,{"Counter"},"Expanded Column1",JoinKind.LeftOuter),
    Expand = Table.ExpandTableColumn( MergedQueries, "Expanded Column1", {"ListItem"}, {"RunningTotal"}),
    #"Removed Columns" = Table.RemoveColumns(Expand,{"Index"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Removed Columns",{{"RunningTotal", type number}})
in
    #"Changed Type"

3c – SecOverUnder Index
let
    Source = #"1 - Data Table",
    
    #"Buffered Table" = Table.Buffer(Source),

    //Running Total
    #"Group by CaseNo" = Table.Group(#"Buffered Table", {"CaseNo"}, {{"All", each _, type table}}, GroupKind.Local),
    #"Added Running Total 1" = Table.AddColumn(#"Group by CaseNo","Sec Avg Running Total", each fxSecRunningTotal([All], "CaseNo", "Sec Avg Activity SEI")),

    //Calculate over/under SEI
    #"Added Conditional Column" = Table.AddColumn(#"Added Running Total 1", "Sec OverUnder", each if [Sec Avg Running Total] > [Sec SEI Value] then "Over" else if [Sec Avg Running Total] < [Sec SEI Value] then "Under" else "Equal"),
    #"Changed Type" = Table.TransformColumnTypes(#"Added Conditional Column",{{"Sec Total Avg SEI", type number}, {"Sec Avg Running Total", type number}}),
    #"Sec Avg Running Total" = #"Changed Type"{0}[Sec Avg Running Total]
in
    #"Sec Avg Running Total"