Copying a SUM Value

[Michael Smith]

I have a table with a column called TAX.

I am trying to copy the Sum of that column to another column called TOTTAX.

I am using the code below.

SELECT SUM(TOTAL) AS "TTotal" FROM Invoices01;
Update Invoices01 set TOTTAX = TTotal;

This code does not do anything. I would appreciate any suggestions?

Mike