从MySQL数据库显示PHP中的类别和子类别

Question

I'm trying to display a list of categories and subcatagories on a website that are populated from a MySQL database and I'm a bit rusty with how to do it properly.

Basically I want to achieve this:

Parent Cat 1 
--Child Cat1
--Child Cat2
Parent Cat 2
Parent Cat 3
--Child Cat 1
--Child Cat 2

and the database is layed out:

ParentCat1,   ChildCat1,   Item1
ParentCat1,   ChildCat1,   Item2
ParentCat1,   ChildCat2,   Item1
ParentCat2,                Item1
ParentCat3,   ChildCat1,   Item1
ParentCat3,   ChildCat2,   Item2

EDIT this is what I have so far big thanks to Gowtham:

<?php
    $conn = mysql_connect("localhost", "USER", "PASS");

    if (!$conn) {
        echo "Unable to connect to DB: " . mysql_error();
        exit;
    }

    if (!mysql_select_db("DB-Store")) {
        echo "Unable to select DB-Store: " . mysql_error();
        exit;
    }

    $sql = "SELECT * FROM menu";

    $result = mysql_query($sql);

    if (!$result) {
        echo "Could not successfully run query ($sql) from DB: " . mysql_error();
        exit;
    }

    if (mysql_num_rows($result) == 0) {
        echo "No rows found, nothing to print";
        exit;
    }

    $result = mysql_query($sql);
    $menu = array();
    echo "Start of Array";
    echo "<br>";
    while ($row = mysql_fetch_assoc($result)) {
        $menu['category'][] = $result['cat'];
        if (!empty($result['subcat']))
        $menu['subcat'][$result['cat']][] = $result['subcat'];          
    }

    foreach ($menu['category'] as $cat) {
        echo $cat."<br>";
        foreach ($menu['subcat'][$cat] as $subcat) {
            echo "--" . $subcat."<br>";
        }
    }
    echo "<br>";
    echo "End of Array";
    mysql_free_result($result);
?>

Answer 1

The first thing I will do to achieve it is, getting value from the database and store it in the array and run a loop to print the array.

Here is my code. Let's consider category field name is cat and subcategory field name is subcat and table name is menu, then

<?php

$sql = 'select * from menu';
$con = mysqli_connect("localhost", "my_user", "my_password", "my_db");
// Check connection
if (mysqli_connect_errno()) {
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

// Perform queries
$result = mysqli_query($con, $sql);

$menu = array();
while ($row = mysqli_fetch_assoc($result)) {
    if (!in_array($row['cat'], $menu['category'])) {

            $menu['category'][] = $row['cat'];
    }
    if (!empty($row['subcat']))
        $menu['subcat'][$row['cat']][] = $row['subcat'];
}

foreach ($menu['category'] as $cat) {
    echo $cat."<br>";
    foreach ($menu['subcat'][$cat] as $subcat) {
        echo "--" . $subcat."<br>";
    }
}
?>

And the above program will satisfy your need.