[php] What is the difference between bindParam and bindValue?

What is the difference between PDOStatement::bindParam() and PDOStatement::bindValue()?

The simplest way to put this into perspective for memorization by behavior (in terms of PHP):

• bindParam: reference
• bindValue: variable

For the most common purpose, you should use bindValue.

bindParam has two tricky or unexpected behaviors:

• bindParam(':foo', 4, PDO::PARAM_INT) does not work, as it requires passing a variable (as reference).
• bindParam(':foo', $value, PDO::PARAM_INT) will change $value to string after running execute(). This, of course, can lead to subtle bugs that might be difficult to catch.

Source: http://php.net/manual/en/pdostatement.bindparam.php#94711

From Prepared statements and stored procedures

Use bindParam to insert multiple rows with one time binding:

<?php

$stmt = $dbh->prepare("INSERT INTO REGISTRY (name, value) VALUES (?, ?)");
$stmt->bindParam(1, $name);
$stmt->bindParam(2, $value);

// insert one row
$name = 'one';
$value = 1;
$stmt->execute();

// insert another row with different values
$name = 'two';
$value = 2;
$stmt->execute();

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.

You don't have to struggle any longer, when there exists a way lilke this:

$stmt = $pdo->prepare("SELECT * FROM someTable WHERE col = :val");
$stmt->execute([":val" => $bind]); 

From the manual entry for PDOStatement::bindParam:

[With bindParam] Unlike PDOStatement::bindValue(), the variable is bound as a reference and will only be evaluated at the time that PDOStatement::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'