Re: & and && and weird results NOT solved but FIXED ....

PJ wrote: > Kyle Smith wrote: > >> Kyle Smith wrote: >> >>> PJ wrote: >>> >>>> I hope somebody can make sense of this. >>>> First, I don't understand what the difference is supposed to be between >>>> & and && - is there a difference for php and/or mysql? >>>> Second, I am trying to select all occurrences in a table.column where >>>> the first letter of the name is I, J, or K but not I or J or K; I want >>>> the all. Now, entering the following is no problem for any one letter: >>>> SELECT * FROM book >>>> WHERE id IN (SELECT bookID >>>> FROM book_author WHERE authID IN (SELECT author.id >>>> FROM author >>>> WHERE LEFT(last_name, 1 ) = '$Auth' )); >>>> >>>> But the following does not work: >>>> >>>> SELECT * FROM book >>>> WHERE id IN (SELECT bookID >>>> FROM book_author WHERE authID IN (SELECT author.id >>>> FROM author WHERE LEFT(last_name, 1 ) = '$Auth' && >>>> LEFT(last_name, 1 ) = '$Auth1' && LEFT(last_name, 1 ) = >>>> '$Auth2')); >>>> >>>> Yet this gives off the wall results where the last names are nowhere >>>> near what they should be. >>>> Anyone have a rational explanation? >>>> >>>> >>>> >>> I wasn't aware that && was an option in MySQL, I've always used >>> "AND". If there is a difference it's probably the same as in PHP and >>> many other languages. Allow me to explain. >>> >>> In the case of & the left-side expression is evaluated for true and >>> if not true, the right side expression is not evaluated. In the case >>> of && both sides are evaluated regardless of the value of either >>> side. Here's an example: >>> >>> $a = 1; >>> $b = 2; >>> >>> $result = ($a == 2) && $b++; // In this case, $a does not equal two >>> and therefor the left-side is false, thus the right-side is never >>> evaluated. $b remains 2. >>> >>> $result = ($a == 2) & $b++; >>> // In this case, $a still does not equal two and therefor the >>> left-side is still false, however because we use the '&' operator the >>> right side is evaluated anyway and $b now equals 3. >>> >>> echo $result; >>> // In both cases, $result is false. >>> >>> HTH, >>> Kyle >>> >>> >>> >> Oops, my first paragraph is backwards. I'm sure that was confusing! >> My example is the correct logic for && and &, and the paragraph before >> that is exactly wrong. >> >> > Not really clear... I thought that $b+ would == 3 ; why two + ? > > But this does not explain the weir results I am getting; and BTW, if I > use AND does not work either. > What am I supposed to use to get the results I am looking for? > > I did fix it - it seems that OR does the trick. But I sure would like to understand why & does not work? -- unheralded genius: "A clean desk is the sign of a dull mind. " ------------------------------------------------------------- Phil Jourdan --- pj@ptahhotep.com http://www.ptahhotep.com http://www.chiccantine.com/andypantry.php