Detailed explanation of how to use PHP singleton mode

This article mainly introduces the simple usage of PHP singleton mode, and analyzes the specific implementation methods and usage skills of PHP singleton mode combined with the database operation class instance form. Friends in need can refer to it

The details are as follows ：

<?php
class db {
  public $conn;
  public static $sql;
  public static $instance=null;
  private function __construct(){
    require_once(&#39;db.config.php&#39;);
    $this->conn = mysql_connect($db[&#39;host&#39;],$db[&#39;user&#39;],$db[&#39;password&#39;]);
    if(!mysql_select_db($db[&#39;database&#39;],$this->conn)){
      echo "失败";
    };
    mysql_query(&#39;set names utf8&#39;,$this->conn);
  }
  public static function getInstance(){
  if(is_null(self::$instance)){
    self::$instance = new self();
  }
    return self::$instance;
  }
  /**
  * 查询数据库
  */
  public function select($table,$condition=array(),$field = array()){
    $where=&#39;&#39;;
    if(!empty($condition)){
      foreach($condition as $k=>$v){
        $where.=$k."=&#39;".$v."&#39; and ";
      }
      $where=&#39;where &#39;.$where .&#39;1=1&#39;;
    }
    $fieldstr = &#39;&#39;;
    if(!empty($field)){
      foreach($field as $k=>$v){
        $fieldstr.= $v.&#39;,&#39;;
      }
      $fieldstr = rtrim($fieldstr,&#39;,&#39;);
    } else {
      $fieldstr = &#39;*&#39;;
    }
    self::$sql = "select {$fieldstr} from {$table} {$where}";
    $result=mysql_query(self::$sql,$this->conn);
    $resuleRow = array();
    $i = 0;
    while($row=mysql_fetch_assoc($result)){
      foreach($row as $k=>$v){
        $resuleRow[$i][$k] = $v;
      }
    $i++;
    }
    return $resuleRow;
  }
  //添加一条记录
  public function insert($table,$data) {
    $values = &#39;&#39;;
    $data = &#39;&#39;;
    foreach ($data as $k=>$v) {
      $values .= $k.&#39;,&#39;;
      $datas .= "&#39;$v&#39;".&#39;,&#39;;
    }
    $values = rtrim($values,&#39;,&#39;);
    $datas = rtrim($datas,&#39;,&#39;);
    self::$sql = "INSERT INTO {$table} ({$values}) VALUES ({$datas})";
    if(mysql_query(self::$sql)) {
      return mysql_insert_id();
    } else {
      return false;
    }
  }
  //修改一条记录
  public function update($table,$data,$condition=array()){
    $where=&#39;&#39;;
    if(!empty($condition)) {
    foreach($condition as $k=>$v) {
      $where.=$k."=&#39;".$v."&#39; and ";
    }
      $where=&#39;where &#39;.$where .&#39;1=1&#39;;
    }
    $updatastr = &#39;&#39;;
    if(!empty($data)) {
    foreach($data as $k=>$v) {
      $updatastr.= $k."=&#39;".$v."&#39;,";
    }
      $updatastr = &#39;set &#39;.rtrim($updatastr,&#39;,&#39;);
    }
    self::$sql = "update {$table} {$updatastr} {$where}";
    return mysql_query(self::$sql);
  }
  //删除记录
  public function delete($table,$condition) {
    $where=&#39;&#39;;
    if(!empty($condition)) {
      foreach($condition as $k=>$v) {
        $where.=$k."=&#39;".$v."&#39; and ";
      }
      $where=&#39;where &#39;.$where .&#39;1=1&#39;;
    }
    self::$sql = "delete from {$table} {$where}";
    return mysql_query(self::$sql);
  }
  public static function getLastSql() {
    echo self::$sql;
  }
}
$db = db::getInstance();
//$list = $db->select(&#39;demo&#39;,array(&#39;name&#39;=>&#39;tom&#39;,&#39;password&#39;=>&#39;ds&#39;),array(&#39;name&#39;,&#39;password&#39;));
//echo $db->insert(&#39;demo&#39;,array(&#39;name&#39;=>&#39;最近你啦&#39;,&#39;password&#39;=>&#39;123&#39;));
//echo $db->update(&#39;demo&#39;,array("name"=>&#39;xxx&#39;,"password"=>&#39;123&#39;),array(&#39;id&#39;=>1));
echo $db->delete(&#39;demo&#39;,array(&#39;id&#39;=>&#39;2&#39;));
db::getLastSql();
echo "<pre class="brush:php;toolbar:false">";
?>

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