What does this function mean in PHP ?

Question

private static function query($query, $params = array()){
$statement = self::connect()->prepare($query);
$statement->execute();
$data = $statement->fetchAll();
return $data;
}

Answer 1

Prepares an SQL statement to be executed by the PDOStatement::execute() method. The SQL statement can contain zero or more named (:name) or question mark (?) parameter markers for which real values will be substituted when the statement is executed. You cannot use both named and question mark parameter markers within the same SQL statement; pick one or the other parameter style. Use these parameters to bind any user-input, do not include the user-input directly in the query.

You must include a unique parameter marker for each value you wish to pass in to the statement when you call PDOStatement::execute(). You cannot use a named parameter marker of the same name more than once in a prepared statement, unless emulation mode is on.

Note:

Parameter markers can represent a complete data literal only. Neither part of literal, nor keyword, nor identifier, nor whatever arbitrary query part can be bound using parameters. For example, you cannot bind multiple values to a single parameter in the IN() clause of an SQL statement.

Calling PDO::prepare() and PDOStatement::execute() for statements that will be issued multiple times with different parameter values optimizes the performance of your application by allowing the driver to negotiate client and/or server side caching of the query plan and meta information, and helps to prevent SQL injection attacks by eliminating the need to manually quote the parameters.

PDO will emulate prepared statements/bound parameters for drivers that do not natively support them, and can also rewrite named or question mark style parameter markers to something more appropriate, if the driver supports one style but not the other.