pdo_mysqli is a PHP class to connect to MySQL and perform Very Easy and Safe SQL queries, using any of PDO, or MySQLi extensions. It requires PHP 5.4+.
By default, the class uses MySQLi, if the PHP server not support MySQLi, the class will use PDO. But if you want, you can easily change the class settings to use PDO as default option.
The class uses prepare() and execute() , the data are automatically filtered by PHP and it is added Safely in the MySQL database.
The SQL queries can contain named or question mark placeholders, and the values associated to placeholders are passed separately into an array to the class method that executes the SQL query (the sqlExec() method).

- Bellow it is the code of the class, you can copy it or download it from this link -> Download pdo_mysqli
(The archive contains examples and a "readme.html" file with documentation).
For comments, questions, or any issue related to this PHP class, write on Forum, in the "Scripts from Website" category.

pdo_mysqli Properties and Method

- $conn represents the object instance of pdo_mysqli class.

For SQL queries that affects data in MySQL database, it is indicated to use placeholder names (or question marks) in the SQL statement, and pass the associated values separately into an array. Data will be added Safely in MySQL database.

PDO_MySQLi usage

1. Copy the pdo_mysqli class on your server (for example into a PHP file named "class.pdo_mysqli.php").
2. In the PHP file in which you want to use the class, include it, and create an object instance of the pdo_mysqli class, passing as argument an array with your data for connecting to MySQL database.
<?php
// Array with data for connecting to mysql database
$mysql = array(
 'host'=> 'localhost',
 'user'=> 'root',
 'pass'=> 'password',
 'bdname'=> 'db_name'
);

include('class.pdo_mysqli.php');     // includes the php file with pdo_mysqli class

// creates object with connection to MySQL
$conn = new pdo_mysqli($mysql);
3. Define the SQL query (optional, array with values for placeholders in SQL), and call the sqlExec() method, passing the SQL query string, and optional the array with values. You can use named or question mark placeholders in the SQL statement (see the examples from downloaded archive).
// Select with named placeholder
$sql = "SELECT * FROM table_name WHERE column = :val";
$values = array('val'=>'value');
$rows = $conn->sqlExec($sql, $values);

// OR, Select without placeholders
$sql = "SELECT * FROM table_name WHERE id = 8";
$rows = $conn->sqlExec($sql);

// traverses the array with rows data
foreach($rows AS $row) {
  echo $row['column'];
}

Example 2 (grouping the result set by columns):
// Select to get the columns data
$sql = "SELECT * FROM table_name WHERE column = :val";
$val = array('id'=>2);
$conn->fetch = 'assoc';    //to return data associated to column-name only
$conn->group = 'cols';     //to group the result set by columns
$cols = $conn->sqlExec($sql, $val);

// check if the SQL query succesfully performed
if($cols) {
  // traverses values added in the 'col_name' column
  foreach($cols['col_name'] AS $val) {
    echo '<br>'. $val;
  }
}
else if($conn->error) echo $conn->error;

//reset $group to default value, if I want the next Select to return data grouped by rows
$conn->group = '';

• To change the default connection from MySQLi to PDO, replace "mysqli" with "pdo" value in the CONN_MOD constant, defined in the "class.pdo_mysqli.php" file (line 2).

- When it is performed Select or Show SQL query, the sqlExec() method returns an array with the result set.
- The result set can be gruped by Rows or Columns, according to the value of the $group property.
- The result set can contain data associated to column-name, column-index, or both, according to the value of the $fetch property.
The array can be traversed using foreach() or for() statement.

PDO_MySQLi class code

This class is Free, without assistance. You can use, modify, and publish it freely.
- Click on the code to select it.
<?php
define('CONN_MOD', 'mysqli');  //sets default connection method: 'pdo', or 'mysqli'

// class to connect to MySQL, and perform easily and safe SQL queries
// From -  http://coursesweb.net/php-mysql/
class pdo_mysqli {
  protected $conn_mod ='';    // 'pdo', or 'mysqli'
  protected $conn = false;    // stores the connection to mysql
  protected $conn_data = [];  // to store data for connecting to database
  public $mysql_version ='';  // mysql server version
  public $fetch ='';         // 'assoc' - columns with named index, 'num' - columns numerically indexed, Else - both
  public $group ='';         //If 'cols': returns data grouped by columns; Otherwise, return Select results grouped by Rows. 
  public $affected_rows =0;  // number affected rows for Insert, Update, Delete
  public $num_rows =0;       // number of rows from Select /Show results
  public $num_cols =0;       // number of columns from Select /Show results
  public $last_insertid;     // stores the last ID in an AUTO_INCREMENT column, after Insert query
  public $nr_queries =0;     // to store number of sql queries
  public $error = false;     // to store and check for errors

  function __construct($conn_data){
    $this->conn_data = $conn_data;   //stores connection data to MySQL database
  }

  // to set the connection to mysql, with PDO, or MySQLi
  protected function setConn($conn_data) {
    // sets the connection method, check if can use pdo or mysqli (with MySQLnd)
    if(CONN_MOD == 'mysqli') {
      if(extension_loaded('mysqli') === true && function_exists('mysqli_get_client_stats')) $this->conn_mod ='mysqli';
      else if(extension_loaded('PDO') === true) $this->conn_mod ='pdo';
    }
    else if(CONN_MOD == 'pdo') {
      if(extension_loaded('PDO') === true) $this->conn_mod ='pdo';
      else if(extension_loaded('mysqli') === true && function_exists('mysqli_get_client_stats')) $this->conn_mod ='mysqli';
    }

    if($this->conn_mod == 'mysqli') $this->connMySQLi($conn_data);
    else if($this->conn_mod == 'pdo') $this->connPDO($conn_data);
    else $this->setSqlError('Unable to use PDO or MySQLi');

    //if error, output it
    if($this->error !== false) echo 'Error: '. $this->error;
  }

  // for connecting to mysql with PDO
  protected function connPDO($conn_data) {
    try {
      // Connect and create the PDO object
      $this->conn = new PDO("mysql:host=".$conn_data['host']."; dbname=".$conn_data['bdname'], $conn_data['user'], $conn_data['pass']);

      // Sets to handle the errors in the ERRMODE_EXCEPTION mode
      $this->conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
      $this->mysql_version = str_replace('.', '', $this->conn->getAttribute(PDO::ATTR_SERVER_VERSION));

      // Sets transfer with encoding UTF-8
      $this->conn->exec('SET character_set_client="utf8",character_set_connection="utf8",character_set_results="utf8";');
    }
    catch(PDOException $e) {
      $this->setSqlError($e->getMessage());
    }
  }

  // method that create the connection to mysql with MySQLi
  protected function connMySQLi($conn_data) {
    // if the connection is successfully established
    $this->conn = new mysqli($conn_data['host'], $conn_data['user'], $conn_data['pass'], $conn_data['bdname']);
    if(mysqli_connect_errno()){
      $this->setSqlError('MySQL connection failed: '. mysqli_connect_error());
      $this->conn = false;
    }
    else {
      $this->mysql_version = strval($this->conn->server_version);
      $this->conn->query('SET character_set_client="utf8",character_set_connection="utf8",character_set_results="utf8";');
    }
  }

  // Performs SQL queries
  // $sql - SQL query with prepared statement
  // $param - array of values for SQL query
  public function sqlExec($sql, $param=[]) {
    if($this->conn === false || $this->conn === NULL) $this->setConn($this->conn_data);      // sets the connection to mysql

    // resets previous regstered data
    $this->affected_rows = 0;
    $this->num_rows = 0;
    $this->num_cols = 0;

    // if there is a connection set ($conn property not false)
    if($this->conn !== false){
      // gets the first word in $sql, to determine when SELECT query
      $mode = explode(' ', trim(preg_replace('/[^A-z ]+/i', '', str_ireplace(PHP_EOL, ' ', $sql))), 2);
      $mode = strtolower($mode[0]);
      $this->error = false;   // to can perform current $sql if previous has error
      $nr_p = count($param);  // number of elements for placeholders

      // code to replace ":placeholder" with "?" (for MySQLi)
      if($this->conn_mod == 'mysqli') {
        // check if number of :placeholders match number of items in $param. If they match, replace :placeholder with ? (for MySQLi)
        // else, replace :placeholder with its value, and empty $param
        if(preg_match_all('/:[^,|"|\'|;|\)\} ]*/i', $sql, $mt)){
          $nr_m = count($mt[0]);
          if($nr_p == $nr_m) $sql = preg_replace('/:[^,|"|\'|;|\)\} ]*/i','?', $sql);
          else {
            foreach($param AS $k => $v) {
              if(is_string($v)) $v = "'". str_replace("'", "\\'", $v) ."'";
              $sql = str_ireplace(':'. $k, $v, $sql);
            }
            $param = [];  $nr_p = 0;
          }
        }
      }

      $sqlre = $this->conn->prepare($sql);  // prepares statement

      // if successfully prepared execute query
      if(is_object($sqlre)){
        if($this->conn_mod == 'mysqli'){
          // if values in $param, sets to use "bind_param" before execute()
          if($nr_p >0){
            // stores in $args[0] the type of the value of each value in $param, the rest of items in $args are the values
            $args = [''];
            foreach($param AS $k=>$v) {
              if(is_int($v)) $args[0] .= 'i';
              else if(is_double($v)) $args[0] .= 'd';
              else $args[0] .= 's';
              $args[] = &$param[$k];
            }

            // binds the values with their types in prepared statement
            call_user_func_array([$sqlre,'bind_param'], $args);
          }

          if(!$sqlre->execute()) {
            if(isset($this->conn->error_list[0]['error'])) $this->setSqlError($this->conn->error_list[0]['error']);
            else $this->setSqlError('Unable to execute the SQL query, check if values are passed to sqlExec()');
          }
        }
        else if($this->conn_mod == 'pdo'){
          try { $sqlre->execute($param); }
          catch(PDOException $e) { $this->setSqlError($e->getMessage()); }
        }

        $this->nr_queries++;    // to know number of sql queries
      }
      else {
        if(isset($this->conn->error_list[0]['error'])) $this->setSqlError($this->conn->error_list[0]['error']);
        else $this->setSqlError('Unable to prepare the SQL query, check if SQL query data are correctly');
      }

      // if no error
      if($this->error === false) {
        // if $mode is 'select' or 'show', gets the result_set to return
        if($mode == 'select' || $mode == 'show') {
          $re = ($this->conn_mod == 'mysqli') ? $this->getSelectMySQLi($sqlre) : $this->getSelectPDO($sqlre);  // gets select results

          //set number of rows and items
          $nr_i = count($re);  // number of items in results
          if(isset($re[0])) { $nr_i2 = ($this->fetch != 'assoc' && $this->fetch != 'num') ? count($re[0]) /2 :  count($re[0]); }
          else $nr_i2 =0;
          if($this->group !='cols') {$this->num_rows = $nr_i; $this->num_cols = $nr_i2;}
          else {$this->num_rows = $nr_i2; $this->num_cols = $nr_i;}
        }
        else { $re = true; $this->affected_rows = ($this->conn_mod == 'mysqli') ? $sqlre->affected_rows : $sqlre->rowCount(); }  // affected rows for Insert, Update, Delete

        // if Insert query, stores the last insert ID
        if($mode == 'insert') $this->last_insertid = ($this->conn_mod == 'mysqli') ? $this->conn->insert_id : $this->conn->lastInsertId();
      }
    }

    // sets to return false in case of error
    if($this->error !== false) $re = false;
    return $re;
  }

  // gets and returns Select results performed with PDO
  // receives the object created with prepare() statement
  protected function getSelectPDO($sqlre) {
    $re = [];

    // if fetch() returns at least one row (not false), adds the rows in $re, according to $fetch property
    $fetch = $this->fetch =='assoc' ? PDO::FETCH_ASSOC :($this->fetch =='num' ? PDO::FETCH_NUM : PDO::FETCH_BOTH);
    if($row = $sqlre->fetch($fetch)){
      do {
        // check each column if it has numeric value, to convert it from "string"
        foreach($row AS $k=>$v){
          if(is_numeric($v)) $row[$k] = $v + 0;
          if($this->group =='cols'){  //store by cols
            if(!isset($re[$k])) $re[$k] =[];
            $re[$k][] = $v;
          }
        }
        if($this->group !='cols') $re[] = $row;  //store by rows
      }
      while($row = $sqlre->fetch($fetch));
    }
    return $re;
  }

  // gets and returns Select results performed with MySQLi
  // receives the object created with prepare() statement
  protected function getSelectMySQLi($sqlre) {
    $re = [];
    $result = $sqlre->get_result();  //get result set from a prepared /execute statement

    // gets array with results according to $fetch
    $fetch = $this->fetch =='assoc' ? MYSQLI_ASSOC :($this->fetch =='num' ? MYSQLI_NUM : MYSQLI_BOTH);
    while($row = $result->fetch_array($fetch)){
      if($this->group !='cols') $re[] = $row;  //get by rows
      else {  //get by columns
        foreach($row AS $k=>$v){
          if(!isset($re[$k])) $re[$k] =[];
          $re[$k][] = $v;
        }
      }
    }
    return $re;
  }

  // set sql error in $error
  protected function setSqlError($err) {
    $this->error = $err ;
  }
}

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which attribute is used in <a> tag for the address of the link?
src href rel
<a href="http://coursesweb.net/" title="CoursesWeb.net">CoursesWeb.net</a>
Which CSS property sets the type of the text font?
font-family text-decoration font-size
h2 {
  font-family:"Calibri",sans-serif;
}
What instruction selects all the <div> tags with class="cls"?
querySelector("div.cls") getElementsByTagName("div") querySelectorAll("div.cls")
var elm_list = document.querySelectorAll("div.cls");
var nr_elms = elm_list.length;       // number of selected items
alert(nr_elms);
Indicate the function that can be used to get the sum of values in an array.
array_sum() array_diff() array_shift()
$arr = array(1, 2, 3, 4);
$arr_sum = array_sum($arr);
echo $arr_sum;       // 10
PDO_MySQLi class

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