MySQLi面向对象实践--select

Posted 2020-10-24 寻觅beyond

对于update、insert、delete请参考http://www.cnblogs.com/-beyond/p/8457580.html

 

执行select，如果SQL语句执行成功，那么返回的是一个mysqli_result对象，如果SQL语句出错，则返回false。

<?php
    $mysqli = new Mysqli();
    $mysqli->connect("localhost","root","root","test");
    if ( $mysqli->connect_errno ){
        die( $mysqli->connect_error );
    }
    $mysqli->set_charset("utf8");
    $sql = "select * from mysqli;";
    $mysqli_result = $mysqli->query($sql);
    if( ! $mysqli_result ){
        echo "error:".$mysqli->errno." : ".$mysqli->error;
    } else {
        print_r( $mysqli_result ); //打印查看会是一个mysqli_result对象
    }
    $mysqli->close();
?>

　　结果如下：

mysqli_result Object
(
    [current_field] => 0
    [field_count] => 2
    [lengths] =>
    [num_rows] => 3
    [type] => 0
)

　　上面的这几项都是mysqli_result类的成员属性，都是可以通过mysqli_result的对象加 ->属性访问，比如查看结果集的条数 

<?php
    $mysqli = new Mysqli();
    $mysqli->connect("localhost","root","root","test");
    if ( $mysqli->connect_errno ){
        die( $mysqli->connect_error );
    }
    $mysqli->set_charset("utf8");
    $sql = "select * from mysqli;";
    $mysqli_result = $mysqli->query($sql);
    if( ! $mysqli_result ){
        echo "error:".$mysqli->errno." : ".$mysqli->error;
    } else {
        echo $mysqli_result->num_rows;
    }
    $mysqli->close();
?>

　　

获取完整结果集

　　使用mysql_result::fetch_all([fetch_type])方法获取一个索引数组的结果集，该结果集为完整的结果集；

　　参数fetch_type可以为MYSQLI_NUM（索引数组，默认）、MYSQLI_ASSOC（关联数组)、MYSQLLI_BOTH（两者都要），但是这个方法只适用于mysqlnd，mysqlnd在PHP5.4以后已经作为默认驱动，

<?php
    $mysqli = new Mysqli();
    $mysqli->connect("localhost","root","root","test");
    if ( $mysqli->connect_errno ){
        die( $mysqli->connect_error );
    }
    $mysqli->set_charset("utf8");
    $sql = "select * from mysqli;";
    $mysqli_result = $mysqli->query($sql);
    if( $mysqli_result && $mysqli_result->num_rows>0 ){
        $res = $mysqli_result->fetch_all();
        print_r($res);
    } else {
        echo "error:".$mysqli->errno." : ".$mysqli->error;
    }
    $mysqli->close();
?>

　　结果如下：

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => aaaa
        )

    [1] => Array
        (
            [0] => 2
            [1] => bbbb
        )

)

　

获取一条结果集

　　移动内部指针：mysqli_result::data_seek( int offset ) 只需指定offset值即可。

　　使用mysqli_result::fetch_row()来获取“指针所值”的一条数据，每取一次数据，指针指向下一条记录，结果以索引数组返回。

　　使用mysqli_result::fetch_array([fetch_type])，参数fetch_type可以为MYSQLI_NUM（索引数组）、MYSQLI_ASSOC（关联数组)、MYSQLLI_BOTH（两者都要，默认）

　　使用mysqli_result::fetch_assoc()来获取一条数据，和fetch_row类似，只不过返回的结果集是以关联数组形式。

　　还可以使用fetch_object()以一个对象的形式返回。

<?php
    $mysqli = new Mysqli();
    $mysqli->connect("localhost","root","root","test");
    if ( $mysqli->connect_errno ){
        die( $mysqli->connect_error );
    }
    $mysqli->set_charset("utf8");
    $sql = "select * from mysqli;";
    $mysqli_result = $mysqli->query($sql);
    if( $mysqli_result && $mysqli_result->num_rows>0 ){

        $res = $mysqli_result->fetch_row();
        print_r( $res ); //Array ( [0] => 1 [1] => aaaa )

        $mysqli_result->data_seek(0);
        $res = $mysqli_result->fetch_array();
        print_r( $res ); //Array ( [0] => 1 [id] => 1 [1] => aaaa [name] => aaaa )

        $mysqli_result->data_seek(0);
        $res = $mysqli_result->fetch_assoc();
        print_r( $res ); //Array ( [id] => 1 [name] => aaaa )

    } else {
        echo "error:".$mysqli->errno." : ".$mysqli->error;
    }
    $mysqli->close();
?>

　　

释放结果集

　　mysqli_result::free

　　mysqli_result::close

　　mysqli_result::free_result

　　这三者都可以

 

遍历结果集

在遍历结果集之前可以先判断结果集中是否有记录。

方法一：一次性获取（fetch_all)，然后循环遍历

<?php
    $mysqli = new Mysqli();
    $mysqli->connect("localhost","root","root","test");
    if ( $mysqli->connect_errno ){
        die( $mysqli->connect_error );
    }
    $mysqli->set_charset("utf8");
    $sql = "select * from mysqli;";
    $mysqli_result = $mysqli->query($sql);
    if( $mysqli_result && $mysqli_result->num_rows>0 ){
        $res = $mysqli_result->fetch_all();//一次性去的所有数据
        foreach( $res as $row ) {
            print_r( $row );
        }
        $mysqli_result->free_result(); //释放结果集
    } else {
        echo "error:".$mysqli->errno." : ".$mysqli->error;
    }
    $mysqli->close();
?>

　　

方法二：循环获取(fetch_array、fetch_assoc、fetch_row）

<?php
    $mysqli = new Mysqli();
    $mysqli->connect("localhost","root","root","test");
    if ( $mysqli->connect_errno ){
        die( $mysqli->connect_error );
    }
    $mysqli->set_charset("utf8");
    $sql = "select * from mysqli;";
    $mysqli_result = $mysqli->query($sql);
    if( $mysqli_result && $mysqli_result->num_rows>0 ){
        while( $row = $mysqli_result->fetch_assoc() ){
            print_r( $row );
        }
        $mysqli_result->free_result(); //释放结果集
    } else {
        echo "error:".$mysqli->errno." : ".$mysqli->error;
    }
    $mysqli->close();
?>