Multiply two columns in a select

Question

I have two columns (valor_unitario and quantidade) wanted to make a select that multiplied all columns in the field valor_unitario * quantidade.

Example:

Valor_Unit|Quantidade
    15    *    2
          +
    10    *    1

Result: 40

Answer 1

Basically it is only necessary to perform a SUM upon their multiplication of the columns:

SELECT SUM((Valor_Unit * Quantidade)) AS total
  FROM tabela