Update a table from sum(field) from another table

[Balakrishnan Kaliyamoorthy]

Dear All,

I want to update a field's value in a table with sum(field1) from another table.
For eg. I am having 2 tables. Table1, Table2.

Structure of Table1 as follows.
OrderID Integer,
OrderTotal Float

Structure of table2 as follows.
OrderID integer,
ProductID Varchar(40),
UnitPrice Float,
Quantity Integer

I want to update table1's ordertotal with sum(Quantity * UnitPrice) from Table2.

Regard,
Balakruishnan.K