What to do if php query fails

Solution to PHP query failure: 1. Use the function "mysql_select_db('demo');" to select the query database; 2. Add a database resource connector to mysql_query.

The operating environment of this article: Windows 7 system, PHP version 7.1, DELL G3 computer

What should I do if the php query fails?

The specific problem is described as follows:

php+mysql! 连接成功，但是查询失败！
详细代码如下：
<?php
$startTime=microtime (true);
//打开数据库
$mysql=mysql_connect(&#39;127.0.0.1 : 3306&#39;,&#39;root&#39;,&#39;root123&#39;,&#39;demo&#39;);
if (!$mysql){
echo "连接失败，原因为：".mysql_error();
exit();
}
//读取student表
$query = mysql_query("select * from student") or die("查询失败");
//关闭数据库
mysql_close($mysql );
?>
mysql本地有student表 表中也有数据，在mysql中可以查询 但是mysql不能查询，显示查询失败 我的平台是win7 +apache +mysql +php！谢谢哈 在线等！
各位大侠多谢帮忙哈 本人穷 没有分 还望海涵 纯技术问题。。。
lingquery语句换成show databases 是可以看到里面四个数据库的，分别是
infomation_schema
demo
mysql
test
但是连接demo数据库后查询student表，显示查询失败，但是student表里面是有内容的

Solution:

There are 2 reasons for failure:

1. mysql_connect('127.0.0.1 : 3306','root','root123','demo');

The demo here is a database that cannot be connected to. The function mysql_select_db('demo') should be used;

2. mysql_query("select * from student") or die("query failed");

The mysql_query here requires a database resource Connector (i.e. $mysql)

If you correct the above 2 points, you should not go wrong!

Recommended learning: "PHP Video Tutorial"

The above is the detailed content of What to do if php query fails. For more information, please follow other related articles on the PHP Chinese website!