MySQL OR operator
MySQL OR operator compares two expressions and returns TRUE if either of the expressions is TRUE.
When more than one logical operator is used in a statement, OR operators perform after AND operator. The order of evaluation can be changed by using parentheses.
The operator returns 1 when both operands are a non-NULL and one of them is nonzero and returns 0 when both operands are non-NULL and one of them is zero and returns NULL when one operand is NULL and other is zero and return 1 also when one is NULL and another operand is nonzero and NULL also when both operands and NULL.
MySQL Version: 5.6
Example: MySQL OR operator
The following MySQL statement satisfies the condition — «both operands are a non-NULL and one of them is nonzero», so it returns 1.
Sample Output:
MySQL> SELECT 5 || 5; +--------+ | 5 || 5 | +--------+ | 1 | +--------+ 1 row in set (0.00 sec)
Example of MySQL OR operator with at least one (zero) 0
The following MySQL statement satisfies the condition — «both operands are non-NULL and one of them is zero», so it returns 1.
Sample Output:
MySQL> SELECT 5 || 0; +--------+ | 5 || 0 | +--------+ | 1 | +--------+ 1 row in set (0.00 sec)
Example of MySQL OR operator when both operands are zero(0)
The following MySQL statement both of the operands are 0, so it returns 0.
Sample Output:
MySQL> SELECT 0 || 0; +--------+ | 0 || 0 | +--------+ | 0 | +--------+ 1 row in set (0.00 sec)
Example of MySQL OR operator with at least one NULL operand
The following MySQL statement satisfies the condition — «one operand is NULL and other is zero», so it returns NULL.
Sample Output:
MySQL> SELECT 0 || NULL; +-----------+ | 0 || NULL | +-----------+ | NULL | +-----------+ 1 row in set (0.01 sec)
Example of MySQL OR operator with NULL and non-zero operand
The following MySQL statement satisfies the condition — «one operand is NULL and other is non-zero», so it returns 1.
Sample Output:
MySQL> SELECT 5 || NULL; +-----------+ | 5 || NULL | +-----------+ | 1 | +-----------+ 1 row in set (0.00 sec)
Example of MySQL OR operator with both NULL operands
The following MySQL statement both of the operands are NULL, so it returns NULL.
Sample Output:
MySQL> SELECT NULL || NULL; +--------------+ | NULL || NULL | +--------------+ | NULL | +--------------+ 1 row in set (0.00 sec)
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Or operator in mysql php
worth reading for people learning about php and programming: (adding extras to get highlighted code)
about the following example in this page manual:
Example#1 Logical operators illustrated
.
// «||» has a greater precedence than «or»
$e = false || true ; // $e will be assigned to (false || true) which is true
$f = false or true ; // $f will be assigned to false
var_dump ( $e , $f );
// «&&» has a greater precedence than «and»
$g = true && false ; // $g will be assigned to (true && false) which is false
$h = true and false ; // $h will be assigned to true
var_dump ( $g , $h );
?>
_______________________________________________end of my quote.
If necessary, I wanted to give further explanation on this and say that when we write:
$f = false or true; // $f will be assigned to false
the explanation:
«||» has a greater precedence than «or»
its true. But a more acurate one would be
«||» has greater precedence than «or» and than «=», whereas «or» doesnt have greater precedence than » default»>$f = false or true ;
If you find it hard to remember operators precedence you can always use parenthesys — «(» and «)». And even if you get to learn it remember that being a good programmer is not showing you can do code with fewer words. The point of being a good programmer is writting code that is easy to understand (comment your code when necessary!), easy to maintain and with high efficiency, among other things.
Evaluation of logical expressions is stopped as soon as the result is known.
If you don’t want this, you can replace the and-operator by min() and the or-operator by max().
c ( a ( false ) and b ( true ) ); // Output: Expression false.
c ( min ( a ( false ), b ( true ) ) ); // Output: Expression is false.
c ( a ( true ) or b ( true ) ); // Output: Expression true.
c ( max ( a ( true ), b ( true ) ) ); // Output: Expression is true.
?>
This way, values aren’t automaticaly converted to boolean like it would be done when using and or or. Therefore, if you aren’t sure the values are already boolean, you have to convert them ‘by hand’:
c ( min ( (bool) a ( false ), (bool) b ( true ) ) );
?>
This works similar to javascripts short-curcuit assignments and setting defaults. (e.g. var a = getParm() || ‘a default’;)
( $a = $_GET [ ‘var’ ]) || ( $a = ‘a default’ );
?>
$a gets assigned $_GET[‘var’] if there’s anything in it or it will fallback to ‘a default’
Parentheses are required, otherwise you’ll end up with $a being a boolean.
> > your_function () or return «whatever» ;
> ?>
doesn’t work because return is not an expression, it’s a statement. if return was a function it’d work fine. :/
This has been mentioned before, but just in case you missed it:
//If you’re trying to gat ‘Jack’ from:
$jack = false or ‘Jack’ ;
// Try:
$jack = false or $jack = ‘Jack’ ;
//The other option is:
$jack = false ? false : ‘Jack’ ;
?>
$test = true and false; —> $test === true
$test = (true and false); —> $test === false
$test = true && false; —> $test === false
NOTE: this is due to the first line actually being
due to «&&» having a higher precedence than «=» while «and» has a lower one
If you want to use the ‘||’ operator to set a default value, like this:
$a = $fruit || ‘apple’ ; //if $fruit evaluates to FALSE, then $a will be set to TRUE (because (bool)’apple’ == TRUE)
?>
instead, you have to use the ‘?:’ operator:
$a = ( $fruit ? $fruit : ‘apple’ ); //if $fruit evaluates to FALSE, then $a will be set to ‘apple’
?>
But $fruit will be evaluated twice, which is not desirable. For example fruit() will be called twice:
function fruit ( $confirm ) if( $confirm )
return ‘banana’ ;
>
$a = ( fruit ( 1 ) ? fruit ( 1 ) : ‘apple’ ); //fruit() will be called twice!
?>
But since «since PHP 5.3, it is possible to leave out the middle part of the ternary operator» (http://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary), now you can code like this:
$a = ( $fruit ? : ‘apple’ ); //this will evaluate $fruit only once, and if it evaluates to FALSE, then $a will be set to ‘apple’
?>
But remember that a non-empty string ‘0’ evaluates to FALSE!
$fruit = ‘1’ ;
$a = ( $fruit ? : ‘apple’ ); //this line will set $a to ‘1’
$fruit = ‘0’ ;
$a = ( $fruit ? : ‘apple’ ); //this line will set $a to ‘apple’, not ‘0’!
?>
To assign default value in variable assignation, the simpliest solution to me is:
$v = my_function () or $v = «default» ;
?>
It works because, first, $v is assigned the return value from my_function(), then this value is evaluated as a part of a logical operation:
* if the left side is false, null, 0, or an empty string, the right side must be evaluated and, again, because ‘or’ has low precedence, $v is assigned the string «default»
* if the left side is none of the previously mentioned values, the logical operation ends and $v keeps the return value from my_function()
This is almost the same as the solution from [phpnet at zc dot webhop dot net], except that his solution (parenthesis and double pipe) doesn’t take advantage of the «or» low precedence.
NOTE: «» (the empty string) is evaluated as a FALSE logical operand, so make sure that the empty string is not an acceptable value from my_function(). If you need to consider the empty string as an acceptable return value, you must go the classical «if» way.
In PHP, the || operator only ever returns a boolean. For a chainable assignment operator, use the ?: «Elvis» operator.
JavaScript:
let a = false;
let b = false;
let c = true;
let d = false;
let e = a || b || c || d;
// e === c
$a = false ;
$b = false ;
$c = true ;
$d = false ;
$e = $a ?: $b ?: $c ?: $d ;
// $e === $c
?>
Credit to @egst and others for the insight. This is merely a rewording for (formerly) lost JavaScript devs like myself.
$res |= true ;
var_dump ( $res );
?>
does not/no longer returns a boolean (php 5.6) instead it returns int 0 or 1