PDO::PARAM_BOOL (integer)
Represents a boolean data type.
PDO::PARAM_NULL (integer)
Represents the SQL NULL data type.
PDO::PARAM_INT (integer)
Represents the SQL INTEGER data type.
PDO::PARAM_STR (integer)
Represents the SQL CHAR, VARCHAR, or other string data type.
PDO::PARAM_LOB (integer)
Represents the SQL large object data type.
PDO::PARAM_STMT (integer)
Represents a recordset type. Not currently supported by any drivers.
Specifies that the parameter is an INOUT parameter for a stored procedure. You must bitwise-OR this value with an explicit PDO::PARAM_* data type.

http://stackoverflow.com/questions/3168 … parameters