更新
mysqli连接，推荐

$conn = mysqli_connect('127.0.0.1','root2','root2');
mysqli_select_db($conn,'jianshu');
$sql = "select * from posts";
$result = mysqli_query($conn,$sql);
while($row = mysqli_fetch_assoc($result)){
var_dump($row);}

处理错误

mysqli_connect_errno()错误代码
mysqli_connect_error()错误内容
if (!$link) {
exit('error('.mysqli_connect_errno().'):'.mysqli_connect_error());//不继续向下执行
//die
}

设定字符集

mysqli_set_charset($conn,'utf8');

取值

mysqli_fetch_all
mysqli_fetch_array
mysqli_fetch_assoc
mysqli_fetch_num

//mysqli_fetch_array默认返回MYSQLI_BOTH
//MYSQLI_ASSOC、 MYSQLI_NUM 、MYSQLI_BOTH默认
//[0] => 34 [id] => 34 [1] =>Linux常用技巧 [title] => Linux常用技巧
print_r(mysqli_fetch_all($result));

mysqli_fetch_array//默认返回两种MYSQLI_BOTH
//MYSQLI_ASSOC MYSQLI_NUM MYSQLI_BOTH默认
//[0] => 34 [id] => 34 [1] =>Linux常用技巧 [title] => Linux常用技巧
print_r(mysqli_fetch_array($result,MYSQLI_NUM));

mysqli_fetch_num
//获取查询结果中的一条数据，为索引数组（数据库第一条，不一定是最小或最大id）
//执行后，指向下一条数据
// [0] => 34 [1] => Linux常用技巧 [2] => 28echo
print_r(mysqli_fetch_row($result));

mysqli_fetch_assoc
//获取查询结果中的一条数据，为关联数组（数据库第一条，不一定是最小或最大id）
//执行后，指向下一条数据
// [id] => 34[title] => Linux常用技巧 [read] => 28echo print_r(mysqli_fetch_assoc($result));

关闭资源、关闭数据库

mysqli_free_result($result);//释放结果资源
mysqli_close($conn); //关闭数据库连接

mysql连接（不推荐）

$link = mysql_link('localhost','root','123') or die('error');
my_select_db('user',$link) or die('error');
$sql = "";
$result = mysql_query($sql);
$count = mysql_num_rows($result);
while($row = mysql_fetch_assoc($result)){
echo $row['id'];
}

以前的

1、连接（mysqli方式）

$con = new mysqli("localhost", "username", "password", "databasename");

2、查询

	$con->query('set names utf8;'); 
	$sql = "SELECT * FROM tablename";  
	$result = $con->query($sql);  
	$data=array();
	while ($tmp=mysqli_fetch_assoc($result)) {
		$data[]=$tmp;
	}
	var_dump($data);

3、插入

	$con->query('set names utf8;');
    $sql="INSERT INTO tablename (name,telphone) VALUES ('name','telphone')";
	if($result = $con->query($sql)){
        echo "成功";
	}else{
		echo "失败";
	}