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.


Questions and Solutions using Arithmetic Operations:



  1. Create a column that divides the standard_amt_usd by the standard_qty to find the unit price for standard paper for each order. Limit the results to the first 10 orders, and include the id and account_id fields.


  1. SELECT id, account_id, standard_amt_usd/standard_qty AS unit_price
FROM orders
LIMIT 10;

2. Write a query that finds the percentage of revenue that comes from poster paper for each order. You will need to use only the columns that end with _usd. (Try to do this without using the total column.) Display the id and account_id fields also. NOTE - you will receive an error with the correct solution to this question. This occurs because at least one of the values in the data creates a division by zero in your formula.

  1. SELECT id, account_id, 
       poster_amt_usd/(standard_amt_usd + gloss_amt_usd + poster_amt_usd) AS post_per
FROM orders
LIMIT 10;


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