The difference between them is in the order of precedence of each.

Order of precedence? But what?!

For example, let's take the mathematical expression 3 + 4 * 2 . What is the result of the expression? 14 or 11? The answer is 11 , because the * operator has a higher precedence than the + operator.

In this case of && , || , and and or , the first two have greater precedence over the other two, otherwise, are identical.

In PHP there are also the & and | operators, but these make bit-a-bit comparisons and between references, instead of the others quoted, that perform logical operations themselves.

This image illustrates well the difference between both logical operators >.

BothoperatorsresultinaBooleanvalueietrueorfalse.

And:$aand$b:Returnstrueifbothpastvaluesaretrue.

Or:$aand$b:Returnstrueif$aor$baretrue.

Xor:$axor$b:Althoughyouhavenotquotedthisoperator,itissimilartoOr,returnstrueif$aor$baretruebutnotboth.

!:!$a:Unaryoperator,returnstrueif$aisnottrue.

&&:$a&&$b:Binaryoperator,returnstrueifboth$aand$baretrue.

OperatorPrecedence

Asexplainedinthe mutley response , the difference between these operators is in the precedence between them, ie which operator is evaluated first and which will be evaluated next, as you can see in the following table, both $a || $b and $a have priority over $b and && .

The following table shows the precedence of the operators, from the highest precedence in the beginning to the lowest precedence.

Example

//ANDvar_dump(7==7AND9>7);//TRUE,ambasasexpressõessãoverdadeirasvar_dump(7==7AND9<7);//FALSE,apenasaprimeiraexpressãoéverdadeira//ORvar_dump(7==7OR9>7);//TRUE,ambasasexpressõessãoverdadeirasvar_dump(7!=7OR9>7);//TRUE,asegundaexpressãoéverdadeiravar_dump(7!=7OR9<7);//FALSE,ambasasexpressõessãofalsas//XORvar_dump(7==7XOR9>7);//FALSE,ambasasexpressõessãoverdadeirasvar_dump(7==7XOR9<7);//TRUE,aprimeiraexpressãoéverdadeiravar_dump(7<7XOR9>7);//TRUE,asegundaexpressãoéverdadeira//!var_dump(!9<7);//TRUE,9NÃOémenorque7var_dump(!9>7);//FALSE,9émaiorque7//&&var_dump(7==7&&9>7);//TRUE,ambasasexpressõessãoverdadeirasvar_dump(7==7&&9<7);//FALSE,apenasaprimeiraexpressãoéverdadeira//||var_dump(7==7||9>7);//TRUE,ambasasexpressõessãoverdadeirasvar_dump(7!=7||9>7);//TRUE,asegundaexpressãoéverdadeiravar_dump(7!=7||9<7);//FALSE,ambasasexpressõessãofalsas

Demo

Reference: Operators of comparison, logical operators and the precedence of operators in PHP

This is logical operators always results in a value of type Boolean ( true or false ) and are widely used where conditional expression is expected.

&& results in true if both of its operands are true, so it is common for these operands to be relational .

|| results in true if at least one of the two operands is true.

and and or are the equivalent of previous operators but have a precedence smaller.

As the documentation shows in the first case the interpretation is this:

($e = (false || true))

In the second case it looks like this:

(($f = false) or true)

So in the first case the conditional expression using the || operator is more important and executes first. In the second case the second operand functions as something additional, the important one is the previous assignment expression. This example does nothing useful, because $f = false will always work and true will never run.

Here comes a curiosity that not everyone knows. These operators work in the form of short circuit, ie if it can already anticipate the final result it does not continue to run. In the case of or if the first expression is already considered true, the second does not need to be executed any more, with a or just one of the two expressions being true. With and the opposite occurs, if the first expression is false, the second does not have to be executed since it is impossible for the final result to be true, remembering that a and requires that both expressions must be true to result in true.

The && and || operators have higher precedence over and and or . This determines the order in which they will run. && and || are executed before and and or .

Manual Link