PL/SQL is faster than SQL – Just ask Mitch.

After their comprehensive defeat at Lord’s back in June, some experts were confidently predicting that Australia would be on the wrong-end of a clean sweep in both of the back-to-back Ashes series.
Mitchell Johnson, if he was mentioned at all, was written off by all and sundry. After all, not only did he not hand homework in on time, he couldn’t be relied upon to hit a barn door, let alone a set of stumps.
Fast-forward a few months and you can see that conventional wisdom has held…to the extent that no barn doors have been dented.
Unfortunately, the same cannot be said of English pride.
Mitch and his mates have a bit of time on their hands before Australia visit South Africa next month – that nice Mr Lehman has let the class off homework – so they’re free to assist in contradicting another of those things that “everyone knows” – SQL is always faster than PL/SQL.

What we’re going to cover here (among other things) is :

  • a quick overview of the LOG ERRORS mechanism (Mitch doesn’t do any other speed)
  • a recap of the older PL/SQL SAVE EXCEPTIONS
  • performance comparison between the two with errors present
  • Explore the limits of LIMIT
  • performance comparison when no errors are present

Mitch is standing at the top of his run. A random English batsmen is quaking at the crease, so let’s get started… Continue reading

Implicit Cursors are from Venus, Explicit Cursors are from Mars

Domestic bliss. There’s nothing like it. There’s certainly nothing like it in our house, particularly when I indulge in one of my endearing little foibles that is guaranteed to get Deb pouting like Angelina Jolie suffering a nasty reaction to a wasp-sting.
Whether it’s leaving the toilet seat up, or hanging my clothes up on the nearest floor, there are some days where I just can’t seem to do anything right.
Having said that, I must confess that I myself, am not a model of toleration. My own personal pout trigger is a query that looks something like this :

SELECT NVL(COUNT(*), 0)
FROM some_table;

I’ve seen this quite a bit recently, usually in the form of an explicit cursor.
Once I’ve got the rant about this out of my system, I’ll then look at how you might make single-row sub-queries a bit more efficient without ending up knee-deep in implicit cursors.
I’ll also ponder what it actually is that we really know about cursors. Continue reading