How to determine whether there is data in php mysql

php Mysql method to determine whether there is data: 1. Create a PHP sample file; 2. Get the number of rows in the select result set; 3. Return the number of rows affected by the previous operation; 4. Query through sql The function code can determine whether there is data.

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

php How does mysql determine whether there is data? How does PHP determine whether the query result of an SQL statement is empty?

PHP and mysql, the golden partners, work well together, but occasionally you will encounter some small needs that you don’t know what to do, such as what we are going to talk about today: how to judge the results of SQL statement queries. Is the set empty?

Let’s take querying student information as an example to see how to achieve our needs.

First of all, let’s take a look at what the data stored in our data table “student” looks like;

id　　stuname　　gender　　age　　grade　　class
1　　张三　　　　　男　　　　16　　17　　　　3
2　　李四　　　　　男　　　　15　　18　　　　2
3　　王美丽　　　　女　　　　16　　17　　　　5

Let’s take a look at the sql query function code. We want to set the age to 16 years old All student information is found;

<?php
$sql = "select * from `student` where `age`=&#39;16&#39;;";
$rows = mysql_query($rs);
?>
<ul>
    <?php
        while($rows=mysql_fetch_array($rs)){
    ?>
        <li>姓名：<?php echo $rows[&#39;stuname&#39;];?></li>
        <li>性别：<?php echo $rows[&#39;gender&#39;];?></li>
        <li>年龄：<?php echo $rows[&#39;age&#39;];?></li>
        <li>年级：<?php echo $rows[&#39;grade&#39;];?></li>
        <li>班级：<?php echo $rows[&#39;class&#39;];?></li>
    <?php
        }
    ?>
</ul>

The above is the query function. When the result set is not empty, everything is normal. When the data set is empty, a blank ul will be obtained. Tag,

As a user, I don’t know why I didn’t get the data. At this time, we need to give the user a prompt message, then we need to determine whether the result set is empty!

How to judge whether the result set is empty? There are two methods:

<?php
//方法一 获取select结果集的行数
$rows=mysql_query("select * from `student` where `age`=&#39;16&#39;;");
if (mysql_num_rows($rows) < 1){
echo &#39;查询无数据！&#39;;
}
//方法二 返回上一次操作受影响的行数
$rows=mysql_query("select * from `student` where `age`=&#39;16&#39;;");
if(!mysql_affected_rows()){
    echo &#39;查询无数据！&#39;;
}
?>

Now that we know the method, let’s apply the method to our code and see the effect

//方法一
<?php
$sql = "select * from `student` where `age`=&#39;16&#39;;";
$rows = mysql_query($rs);
?>
<ul>
    <?php
    if (mysql_num_rows($rs) < 1){
        echo &#39;查询无数据！&#39;;
    }else{
        while($rows=mysql_fetch_array($rs)){
    ?>
        <li>姓名：<?php echo $rows[&#39;stuname&#39;];?></li>
        <li>性别：<?php echo $rows[&#39;gender&#39;];?></li>
        <li>年龄：<?php echo $rows[&#39;age&#39;];?></li>
        <li>年级：<?php echo $rows[&#39;grade&#39;];?></li>
        <li>班级：<?php echo $rows[&#39;class&#39;];?></li>
    <?php
        }
    }
    ?>
</ul>
//方法二
<?php
$sql = "select * from `student` where `age`=&#39;16&#39;;";
$rows = mysql_query($rs);
?>
<ul>
    <?php
    if(mysql_affected_rows()){
        while ($rows=mysql_fetch_assoc($rs)){
    ?>
        <li>姓名：<?php echo $rows[&#39;stuname&#39;];?></li>
        <li>性别：<?php echo $rows[&#39;gender&#39;];?></li>
        <li>年龄：<?php echo $rows[&#39;age&#39;];?></li>
        <li>年级：<?php echo $rows[&#39;grade&#39;];?></li>
        <li>班级：<?php echo $rows[&#39;class&#39;];?></li>
    <?php
        }
    }else {
        echo "查无数据！";
    }
    ?>
</ul>

OK, you're done. Now you will get a prompt when the data cannot be found!

Recommended learning: "PHP Video Tutorial"

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