Power Query to Append to Existing Table - excel

Question

I recently switched to PowerQuery to fetch data from various sources. I have loaded my existing data to a table called "masterEntries".
The query I have calls a function to check the last record for each source in "masterEntries" and fetches only newer records.
let
Source = Excel.CurrentWorkbook(){[Name="formsMaster"]}[Content],
#"Changed Type" = Table.TransformColumnTypes(Source,{{"FormName", type text}, {"Form", type text}, {"LastEntry", Int64.Type}}),
#"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", each formEntries([FormName],[LastEntry])),
#"Expanded Custom" = Table.ExpandTableColumn(#"Added Custom", "Custom", {"EntryId", "Field1", "Field2", "Field3", "Field5", "DateCreated"}, {"EntryId", "Field1", "Field2", "Field3", "Field5", "DateCreated"}),
#"Removed Columns" = Table.RemoveColumns(#"Expanded Custom",{"Form", "LastEntry"}),
in
#"Removed Columns"
This query loads the data to a new table. Instead I want to append the data to "masterEntries".
I am trying to do this with PowerQuery and not VBA. PowerQuery has Append Query feature where two or more queries/results can be combined to a new table.
Even a new query to append the resulting table from above query ("latestEntries") to existing table ("masterEntries") will do.
Any ideas on how it can be done with PowerQuery?
EDIT
My original data ("masterEntries") was loaded manually. It is a big table with 400K+ records. I can load it using a query if that is going to help.
Every run of "latestEntries" checks what records are already in "masterEntries" and fetches only newer entries from different sources.
The Append Query method in Power Query is just a connection. It does not append records permanently. That is, when "latestEntries" brings a new set of records, the "masterEntries" loses the records that were in the earlier run of "latestEntries".

Answer 1

This sounds a bit like a request for "incremental load". This is currently not supported by Power Query in Excel. The workaround is to go via a "linkback"-table like described here: http://ms-olap.blogspot.de/2015/05/incremental-data-loads-in-microsoft.html
If your linkback-table exceeds 1,1 Mio rows, you can use JSON-compression like described here: http://www.thebiccountant.com/2016/12/06/how-to-store-tables-longer-than-11-mio-rows-in-excel/
But be aware, that this costs performance.
Both methods "cost" performance, so this technique only makes sense, if you "save" repetitive execution of really heavy transformations (or long loads from the web).

Answer 2

You should add something like this, just change name of Your_Table into table you want to use:
#"Append Query" = Table.Combine({#"Removed Columns", Your_Table})
in
#"Append Query"

Answer 3

Assuming you have some kind of ID, and it is integer, here is the query for the masterEntries table (this is important!):
let
Source = Excel.CurrentWorkbook(){[Name="masterEntries"]}[Content],
Types = Table.TransformColumnTypes(Source,{{"ID", Int64.Type}, {"Value", type number}}),
//Assuming you have integer-type IDs.
//Otherwise you have to order and index records in a view, and query that view.
MaxID = List.Max(Types[ID]),
//if you have ordered index, List.Max() can be substituted with Table.LastN(Types, 1)[ID]{0}
//it may perform better.
TableFromDB = Excel.CurrentWorkbook(){[Name="source"]}[Content], //Replace with database table
GetNewRows = Table.SelectRows(TableFromDB, each [ID] > MaxID),
MergeTables = Table.Combine({Types, GetNewRows})
in
MergeTables