30. Video: Arithmetic Operators

Arithmetic Operators

Derived Columns

Creating a new column that is a combination of existing columns is known as a derived column (or "calculated" or "computed" column). Usually you want to give a name, or "alias," to your new column using the AS keyword.

This derived column, and its alias, are generally only temporary, existing just for the duration of your query. The next time you run a query and access this table, the new column will not be there.

If you are deriving the new column from existing columns using a mathematical expression, then these familiar mathematical operators will be useful:

  1. * (Multiplication)
  2. + (Addition)
  3. - (Subtraction)
  4. / (Division)

Consider this example:

SELECT id, (standard_amt_usd/total_amt_usd)*100 AS std_percent, total_amt_usd
FROM orders
LIMIT 10;

Here we divide the standard paper dollar amount by the total order amount to find the standard paper percent for the order, and use the AS keyword to name this new column "std_percent." You can run this query on the next page if you'd like, to see the output.

Order of Operations

Remember PEMDAS from math class to help remember the order of operations? If not, check out this link as a reminder. The same order of operations applies when using arithmetic operators in SQL.

The following two statements have very different end results:

  1. Standard_qty / standard_qty + gloss_qty + poster_qty
  2. standard_qty / (standard_qty + gloss_qty + poster_qty)

It is likely that you mean to do the calculation as written in statement number 2!

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