Googling for "SQL injection" gets about 4 million hits. The topic excites interest and superstitious fear. This whitepaper dymystifies the topic and explains a straightforward approach to writing database PL/SQL programs that provably guarantees their immunity to SQL injection.
Only when a PL/SQL subprogram executes SQL that it creates at run time is there a risk of SQL injection; and you'll see that it's easier than you might think to freeze the SQL at PL/SQL compile time. Then you'll understand that you need the rules which prevent the risk only for the rare scenarios that do require run-time-created SQL. It turns out that these rules are simple to state and easy to follow.
Bruce Schneier also has a post titled "How to Write Injection-Proof SQL" that has an interesting comment stream attached to it.