Click the Exhibit$($s$)$ button to examine the data from the PO$\_$HEADER and PO$\_$DETAIL tables. Examine the structures of the PO$\_$HEADER and PO$\_$DETAIL tables:

PO$\_$HEADER

$--------------------$

PO$\_$NUM NUMBER NOT NULL

PO$\_$DATE DATE DEFAULT SYSDATE

PO$\_$TOTAL NUMBER$(9,2)$

SUPPLIER$\_$ID NUMBER$(9)$

PO$\_$TERMS VARCHAR$2(25)$

PO$\_$DETAIL

$------------------$

PO$\_$NUM NUMBER NOT NULL

PO$\_$LINE$\_$ID NUMBER NOT NULL

PRODUCT$\_$ID NUMBER NOT NULL,

QUANTITY NUMBER$(3)$ NOT NULL,

UNIT$\_$PRICE NUMBER $(5,2)$ DEFAULT $0$

The primary key of the PO$\_$HEADER table is PO$\_$NUM. The primary key of the PO$\_$DETAIL table is the combination of PO$\_$NUM and PO$\_$LINE$\_$ID$.$ A FOREIGN KEY constraint is defined on the PO$\_$NUM column of the PO$\_$DETAIL table that references the PO$\_$HEADER table. You want to update the purchase order total amount for a given purchase order. The PO$\_$TOTAL column in the PO$\_$HEADER table should equal the sum of the extended amounts of the corresponding PO$\_$DETAIL records. You want the user to be prompted for the purchase order number when the query is executed. When a purchase order is updated, the PO$\_$DATE column shouldPO$\_$HEADER