How Do You Identify ‘Bad SQL’?

"Before you can identify problem SQL in your database, you have to ask the question of what is bad SQL. What criteria do you use when you begin the hunt for problem SQL in your critical systems? Understand that even the seasoned experts disagree on what constitutes efficient and inefficient SQL; so there s no way to sufficiently answer this question to every Oracle professional s satisfaction. What follows are some general criteria you can use when evaluating the output from various database monitors or personal diagnostic scripts" writes Don Burleson in this SQL tuning article.