Comments on Rational Relational: MySQL T-SQL CASE Statement: Bad Language Design

Roland:Thanks :)Very interesting! I didn't know it...

2008-02-23T17:13:20.808+02:00

Roland:
Thanks :)

Very interesting! I didn't know it was defined in this way in the SQL Standard... Good to know.

Probably the standard designers believe you shouldn't be able to "fall through" the case statement, since T-SQL is more sensitive than C when it comes to small programming mistakes - and things should be stricter.

Hi!welcome to the planet!!!I filed the bug you are...

2008-02-22T03:00:42.963+02:00

Hi!

welcome to the planet!!!

I filed the bug you are referring to.

Personally, I don't find it "bad" language design - it is actually pretty good to be informed that a condition was not anticipated (another thing I like about CASE is that it does'nt "fall through like the switch statement in C, java, PHP etc).

On another level, MySQL's behavior here is exactly as defined in the standard (ISO/IEC 9075-4:2003 (E), 13.6 case statement, page 103):

"c) Otherwise, an exception condition is raised: case not found for case statement, and the execution of
the <case statement> is terminated immediately."

So IMO, it can't do better here. What remains is the clunky syntax to suppress the error. It would probably be ugly no matter what noop construct would be available.

;)

Roland Bouman

right.:)

2007-12-20T17:26:55.438+02:00

right.
:)

WHEN 1=1 THEN CALL default(); Will catch all the q...

2007-12-20T17:18:19.765+02:00

WHEN 1=1 THEN CALL default();

Will catch all the queries that don't fit any conditions, just what ELSE should do - so it is not the main point here.

The empty statement you are looking for is this "BEGIN END;" that I mentioned. 1=1 is not a statement by itself.

Can't it swallowSET @var = SELECT var FROM t;CASE ...

2007-12-20T16:51:19.818+02:00

Can't it swallow

SET @var = SELECT var FROM t;
CASE
WHEN @var=1 THEN CALL do_something();
WHEN @var=2 THEN CALL do_something_else();
WHEN 1=1 THEN CALL default();
END CASE;

or maybe just do ELSE 1=1 or some kind of another empty statement
?