The WHERE clause is used to filter records, which is to query the data under our specified conditions

Syntax

Let us use the following example:

Example

The following example will select all FirstNames from the "MyGuests" table ='Mary' row:

<?php
 header("Content-type:text/html;charset=utf-8");    //設(shè)置編碼
 $servername = "localhost";
 $username = "root";
 $password = "root";
 $dbname = "test";
 $con=mysqli_connect($servername, $username, $password, $dbname);
 // 檢測(cè)連接
 if (mysqli_connect_errno())
 {
     echo "連接失敗: " . mysqli_connect_error();
 }
 
 $result = mysqli_query($con,"SELECT * FROM MyGuests
 WHERE FirstName='Mary'");
 
 while($row = mysqli_fetch_array($result))
 {
     echo $row['firstname'] . "----" . $row['lastname'] ."----".$row['email'];
     echo "<br>";
 }
 ?>

Program execution result:

Use where condition to query all the data of FirstName='Mary' come out.

We now use phpadmin to add an Age field to the MyGuests table

The data in the table now looks like this:

Example

We now use the where clause to query those with Age less than 25:

<?php
 header("Content-type:text/html;charset=utf-8");    //設(shè)置編碼
 $servername = "localhost";
 $username = "root";
 $password = "root";
 $dbname = "test";
 $con=mysqli_connect($servername, $username, $password, $dbname);
 // 檢測(cè)連接
 if (mysqli_connect_errno())
 {
     echo "連接失敗: " . mysqli_connect_error();
 }
 
 $result = mysqli_query($con,"SELECT * FROM MyGuests
 WHERE Age<25 ");
 
 while($row = mysqli_fetch_array($result))
 {
     echo $row['firstname'] . "----" . $row['lastname'] ."----".$row['email']."----".$row['Age'];
     echo "<br>";
 }
 ?>

Program running results:

You can also use the following conditions

Logical operators

We query the data of 'firstname'='Julie' and Age=24

<?php
 header("Content-type:text/html;charset=utf-8");    //設(shè)置編碼
 $servername = "localhost";
 $username = "root";
 $password = "root";
 $dbname = "test";
 $con=mysqli_connect($servername, $username, $password, $dbname);
 // 檢測(cè)連接
 if (mysqli_connect_errno())
 {
     echo "連接失敗: " . mysqli_connect_error();
 }
 
 $result = mysqli_query($con,"SELECT * FROM MyGuests
 WHERE Firstname='Julie' AND Age=24 ");
 
 while($row = mysqli_fetch_array($result))
 {
     echo $row['firstname'] . "----" . $row['lastname'] ."----".$row['email']."----".$row['Age'];
     echo "<br>";
 }
 ?>