php中的数据库查询操作

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define ('DB_HOST', 'localhost');
define ('DB_USER', 'root');
define ('DB_PASS', 'root');
define ('DB_NAME', 'php');
define ('DB_CHAR', 'utf8');
$db = @mysqli_connect(DB_HOST, DB_USER, DB_PASS);
if (mysqli_connect_errno($db)) {
    exit('连接失败'.mysqli_connect_error($db));
}
mysqli_select_db($db, DB_NAME);
mysqli_set_charset($db, DB_CHAR);

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$sql = "SELECT name,salary FROM staff";
$sql = "SELECT name AS 姓名,salary AS 工资 FROM staff WHERE age>90";

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$result = mysqli_query($db, $sql);
var_dump($result);die();

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if (false != $result) { //这是写只是语义性更强
    //如果结果集中存在记录,至少有一条
//    if (mysqli_num_rows($result) > 0) {
    //mysqli_affected_rows($db)也可以完成同样的检测工作,注意参数是连接对象$db,不是结果集对象
    if (mysqli_affected_rows($db) > 0) {
//        echo '共计:'.mysqli_num_rows($result).'条记录<br>';
        echo '共计:'.mysqli_affected_rows($db).'条记录~~<br>';

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while($row = mysqli_fetch_array($result, MYSQLI_NUM)){

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while($row = mysqli_fetch_row($result)){

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while($row = mysqli_fetch_array($result, MYSQLI_ASSOC)){

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while($row = mysqli_fetch_assoc($result)){

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while($row = mysqli_fetch_array($result, MYSQLI_BOTH)){

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while($row = mysqli_fetch_array($result)){

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while($row = mysqli_fetch_object($result)){
//            var_export($row);//以字符串方式表示查询结查
            //如果是对象,可以用指向符来访问
            echo $row->name.'--'.$row->salary;
            echo '<hr>';
            //以变量方式表示,表示的内容更加完整丰富
//            var_dump($row);
        }
    } else {
        echo '没有符合条件的记录';
    }
    //查询失败的处理方式
} else {
    //必须要用exit()或die()终止脚本执行,否则后面的语句还会执行并会报错
    exit('查询失败'.mysqli_errno($db).':'.mysqli_error($db));
}

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mysqli_free_result($result);

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mysqli_close($db);