Re: & and && and weird results

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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


--
*Kyle Smith*
UNIX/Linux Systems Administrator
Inforonics, LLC


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