Re: Re: non-perl SQL question

Very clever solution (you see: it pays to have attended math-class!) but only if the field you try to swap is not a primary key field or indexed by "UNIQUE". Then it burps an error: #1062 - Duplicate entry '6' for key 1

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law

Comment on Re: Re: non-perl SQL question Download Code

Replies are listed 'Best First'.
Re: Re: Re: non-perl SQL question by Roger (Parson) on Dec 31, 2003 at 11:59 UTC
Thanks. ;-) I first had this idea 12 years ago, during a first year C programming lecture at University. The professor declared in the class that if you want to swap the values of two variables, you have to do it with a temporary variable: `X=5 Y=6 # to swap X and Y, introduce a temporary variable Z Z=X X=Y Y=Z` [download] I challenged his declaration and provided the following solution ~~in 2 steps~~ without a third variable: `X=X+Y Y=X-Y X=X-Y # I know this solution is not perfect: # when X and Y are big, there is a danger of overflow.` [download] The lecturer was amazed and gave me an 'A' for the subject. grin The solution `set order_id=11-order_id where order_id in (5,6)` is just another variant of the same trick. Update: Thanks rkg to point out the missing bit. My memory got rusty. The original challenge was to swap the values without using a third temporary variable.	[reply] [d/l] [select]
Re: Re: Re: Re: non-perl SQL question by rkg (Hermit) on Dec 31, 2003 at 12:18 UTC
am i missing something? `x=5 y=6 x=x+y # x = 5+ 6 = 11, yes? y=x-y # y = 11 - 6 = 5, yes?` [download]	[reply] [d/l]
Re: Re: Re: Re: non-perl SQL question by CountZero (Bishop) on Jan 01, 2004 at 22:48 UTC
But of course only with numerical values, not with string data. CountZero "If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law	[reply]
Re^4: non-perl SQL question by Anonymous Monk on Jul 09, 2004 at 21:56 UTC
Thanks alot. You saved me now half a year later	[reply]

In Section Seekers of Perl Wisdom


Clear questions and runnable code get the best and fastest answer
	PerlMonks