<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "company";


$conn = new mysqli($servername, $username, $password, $dbname)
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT * FROM musteri WHERE dogumtarih<'1980-01-01' and
dogumtarih>'1990-01-01'";
$result = $conn->query($sql);
?>

$sql = "SELECT *
FROM musteri
WHERE (dogumtarih BETWEEN '1980-01-01' AND '1990-01-01')";