Help with CREATE SELECT Statement

[Carlos Vazquez]

I get this error when I try to execute the following select statement:
"All Parts of a PRIMARY KEY must be NOT NULL; if you need null in a key, use UNIQUE 
instead."

CREATE  TEMPORARY TABLE IF NOT EXISTS
        CashVariances 
(PRIMARY KEY(sUnit))
SELECT 
        sUnit, 
        dSalesDate AS dDate, 
        SUM(nStoreCash) AS aCash, 
        SUM(nBankCash) AS bCash, 
        SUM(nStoreCash) - SUM(nBankCash) AS nDifference
FROM 
        CashBalances 
GROUP by 
        sUnit, 
        dDate 
ORDER BY 
        RIGHT(concat('0',sUnit),4),
        dDate


I created this statement based on this sample from a book:
CREATE TABLE new_tbl (PRIMARY KEY (a)) SELECT a, b, c FROM old_tbl

The thing is that I want the Field "sUnit" to be the PRIMARY KEY and the recordset 
returned by the SELECT Statement does not return NULL values.  I can't find any 
alternatives except for first creating the table and then inserting the records.  If 
it's something wrong in my CREATE SELECT statement, please, let me know.  Any help 
will be really appreciated... 

Thanks in advance,

Carlos Vázquez
Jr. Financial Programmer
MySQL 3.23