What is the difference between bindParam and bindValue?
From the manual entry for PDOStatement::bindParam
:
[With
bindParam
] UnlikePDOStatement::bindValue()
, the variable is bound as a reference and will only be evaluated at the time thatPDOStatement::execute()
is called.
So, for example:
$sex = 'male';
$s = $dbh->prepare('SELECT name FROM students WHERE sex = :sex');
$s->bindParam(':sex', $sex); // use bindParam to bind the variable
$sex = 'female';
$s->execute(); // executed with WHERE sex = 'female'
or
$sex = 'male';
$s = $dbh->prepare('SELECT name FROM students WHERE sex = :sex');
$s->bindValue(':sex', $sex); // use bindValue to bind the variable's value
$sex = 'female';
$s->execute(); // executed with WHERE sex = 'male'
Here are some I can think about :
- With
bindParam
, you can only pass variables ; not values - with
bindValue
, you can pass both (values, obviously, and variables) bindParam
works only with variables because it allows parameters to be given as input/output, by "reference" (and a value is not a valid "reference" in PHP) : it is useful with drivers that (quoting the manual) :
support the invocation of stored procedures that return data as output parameters, and some also as input/output parameters that both send in data and are updated to receive it.
With some DB engines, stored procedures can have parameters that can be used for both input (giving a value from PHP to the procedure) and ouput (returning a value from the stored proc to PHP) ; to bind those parameters, you've got to use bindParam, and not bindValue.