I continue to study hard to pass my first exam for Oracle certification. Right now I am reading a study guide on the SQL and PL/SQL exam. I just finished chapter 1. At first I thought I should skip the early chapters since I already know a little SQL. However I am glad I didn't. I have learned a bunch of tidbits that I want to share with you now.Although I know you could define aliases in a SELECT statement, I hardly ever do it. I also didn't know much of the details of the aliases until now. You can have a space in the alias name if you enclose it in double quotes. You cannot use the alias name in the WHERE clause. But you can use the alias in the ORDER BY clause.
I have seen some seasoned Oracle developers use the EXISTS keyword in queries. And to tell the truth, I was always a little uncomfortable with what they were actually doing. Now I know that EXISTS returns TRUE if at least one record is returned from its expression.
