CONTINUE statement in PL/SQL – or how GOTO can be a useful member of society

Coding Standards, Best Practices, generally accepted truth – these almost always have something to say on the subject of the evil “GOTO” statement.
Invariably, what’s said is don’t use it. Ever. On pain of pain.
It’s the absolute and unequivocal nature of these strictures that I find annoying.
It may be the case that, in the primordial times of Computer Science, before young Larry Ellison dropped out of College, grew a beard and started getting ideas about applying this Relational Theory stuff to a working database, GOTO was abused to create the dreaded “spaghetti code”.
Since that time, any tentative mention of this structure outside of a Basic Program has been met with revulsion.
However, it’s worth noting that, even such luminaries as Kernighan and Ritchie, whilst describing the goto statement in C as “infinitely abusable” do concede that there are times when gotos may find a place.
As things stand right now (at least, if you’re in one of those shops still waiting for 11g), one of those places can be found in PL/SQL.
I think it’s reasonable to compare PL/SQL ( based on Ada, which in turn is based on Pascal) with C due to they’re shared 3-GL ancestry.
Prior to 11g, PL/SQL is missing one of the features common to many 3-GLs – including C – the continue keyword, which allows the programmer the option to skip a single iteration of a loop without all that mucking about with IF-THEN-ELSE.
For example – say we want to loop through an array of numbers but we only want to process the positive numbers in that array and ignore any negative numbers.
In ‘C’, this is fairly straightforward ….

for( i = 0; i < n; i++)
    if( a[i] <= 0)
    ... /* if we get here then the element is positive
        so do stuff to it */

Contrast this with PL/SQL

   IF a(i) > 0 THEN
      -- do stuff to the positive element
   END IF;
   -- not immediately obvious that we do anything with
   -- the negative elements – you have to read through
   -- all of the code to work this out.

So, no continue statement, a bit less clarity. However, now GOTO is out on parole, we have a job for it …

   IF a(i) < 0 THEN
      GOTO continue;
   END IF;
   -- If we get here then the element is positive
   -- so do stuff
<<continue>> -- continue label
      NULL; -- need a statement here to
         -- stop the compiler choking

You may consider this to be a somewhat artifical way of introducing CONTINUE into PL/SQL. All I’ll say to that is – how do you declare BOOLEANs in C ?

#define TRUE 1
#define FALSE 0

About these ads

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s