Php Mysql 简明教程

PHP & MySQL - Handling NULL Example

可以使用 if…​else 条件根据 NULL 值准备查询。

以下示例从外部获取 tutorial_count,然后将其与表中可用值进行比较。

Example

将以下示例复制粘贴为 mysql_example.php:

<html>
   <head>
      <title>Handling NULL</title>
   </head>
   <body>
      <?php
         $dbhost = 'localhost';
         $dbuser = 'root';
         $dbpass = 'root@123';
         $dbname = 'TUTORIALS';
         $mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
         $tutorial_count = null;
         if($mysqli->connect_errno ) {
            printf("Connect failed: %s<br />", $mysqli->connect_error);
            exit();
         }
         printf('Connected successfully.<br />');

         if( isset($tutorial_count )) {
            $sql = 'SELECT tutorial_author, tutorial_count
               FROM  tcount_tbl
               WHERE tutorial_count = ' + $tutorial_count;
         } else {
            $sql = 'SELECT tutorial_author, tutorial_count
               FROM  tcount_tbl
               WHERE tutorial_count IS NULL';
         }
         $result = $mysqli->query($sql);

         if ($result->num_rows > 0) {
            while($row = $result->fetch_assoc()) {
               printf("Author: %s, Count: %d <br />",
                  $row["tutorial_author"],
                  $row["tutorial_count"]);
            }
         } else {
            printf('No record found.<br />');
         }
         $mysqli->close();
      ?>
   </body>
</html>

Output

访问部署在 Apache Web 服务器上的 mysql_example.php, 并验证输出。

Connected successfully.
No record found.