concatenate strings from 2 tables but only if value not already there

[NickCo]

I have a table (TableA) of contacts that i am uploading from Excel.
One column is called 'Sector'.
The field in Excel contains a Sector name which i want to include in the Access Record, but if the record appears on several Excel sheets, sometimes with the same Sector, i get repition of Sector in that field. It should only appear once.
At the moment, i upload to a temp table (TableB).
I have a 3rd table (TableC)
An append query concatenates TableA, a semi-colon, and TableB into TableC .
An update query then updates tableA to the values in TableC.
I can't seem to get criteria to check if Sector in TableB already exists in TableA, if so skip, else add with simicolon.
Any ideas or help would be much appreciated.

[NeoPa]

I'm not very clear on what's repeating where or why. Nevertheless, the following advice should provide a viable way to work it :

1. Get the data so that it's accessible to Access one way or another. The simplest is to link a table to the spreadsheet.
2. Design an APPEND query that uses the DISTINCT predicate to add only unique items to the [Sector] table.
3. Design a separate APPEND query that takes that data from your spreadsheet linked to the [Sector] table on the Sector name and include the reference to add to the field in your TableA instead of the description itself.