By “Good SQL Querying”, I am not referring to “how to make your queries more perfomant.” I am about to go on a mini-rant about how to make readable and self-documenting SQL queries.
One practice that will get me instantly going on a rant is using a comma join. There is NO reason to do the following:
-- uses the sakila sample database SELECT first_name, last_name, address FROM customer,address;
What kind of join did the original author intend? A CROSS JOIN? Or did they really want an INNER JOIN and forget the WHERE clause?
The answer: you do not know for sure; you can only guess. Had the query been
SELECT first_name,last_name,address FROM customer INNER JOIN address;
you would know that the author intended an INNER JOIN; had the query been
SELECT first_name,last_name,address FROM customer CROSS JOIN[Read more...]