PHP MySQL Where Clause

To select only data that matches a specified criteria, add a WHERE clause to the SELECT statement. The following example creates and populates a Customers table using the following SQL commands: 

CREATE TABLE Customers (
   ID   INT AUTO_INCREMENT PRIMARY KEY,
   name VARCHAR(16) NOT NULL );

INSERT INTO Customers (name) VALUES ('Ben'), ('Bart'), ('Mandy'), ('Ella');

and selects customers using the BETWEEN ... AND operator: 

SELECT * FROM Customers WHERE ID BETWEEN $low AND $high;

            
 <html><body>
 <?php
  $servername = "undcsmysql.mysql.database.azure.com";
  $username   = "user.id@undcsmysql";
  $password   = "password";
  $dbname     = "user_id";         # your database or schema
  // Connect to the database.
  $conn       = new mysqli( $servername, $username, $password, $dbname );

  $action =  Drop    Create & populate  
             Select ( ≤ ID ≤ )    
  if ( $action == "Drop" ) {
    // Drop table Customers.
    $conn->query( "DROP TABLE Customers" );
    echo "Table Customers dropped";
  }
  elseif ( $action == "Create & populate" ) {
    // Create table Customers.
    $sql = "CREATE TABLE Customers (
              ID   INT AUTO_INCREMENT PRIMARY KEY,
              name VARCHAR(16) NOT NULL )";
    $conn->query( $sql );
    echo "Table Customers created";

    // Insert customers.
    $sql = "INSERT INTO Customers (name) VALUES
              ('Ben'), ('Bart'), ('Mandy'), ('Ella')";
    $conn->query( $sql );
    echo " Table Customers populated"
  }
  elseif ( $action == "Select" ) {
    // Select customers.
    $sql = "SELECT * FROM Customers WHERE ID BETWEEN $low AND $high";
    $result = $conn->query( $sql );
    while ( $row = $result->fetch_assoc( ) )
      echo $row['ID'] . ", " . $row['name'];
  }
  $conn->close( );
 ?>
 </body></html>