SQL Query duplicating values even using Distinct - php

Question

My query seems to be duplicating the values that are being displayed.
I don't understand why, I have 5 tables
products with an id and category (4 of them), then each category is related to another table where the product_name, price is, then each one of these tables is related to the table called stock, stock is the one where price is.
`
<tr>
<th>Product Name</th>
<th>Quantity</th>
<th>Price</th>
<th>Action</th>
</tr>
<?php
$conn = mysqli_connect("localhost:3307", "root", "", "db_login");
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT products.id, products.category, hygiene.product_name, hygiene.price, stock.quantity
FROM products
LEFT JOIN hygiene ON products.id = hygiene.product_id
LEFT JOIN stock ON hygiene.product_id = stock.item_id
WHERE products.category = 'Hygiene'
UNION
SELECT products.id, products.category, food.product_name, food.price, stock.quantity
FROM products
LEFT JOIN food ON products.id = food.product_id
LEFT JOIN stock ON food.product_id = stock.item_id
WHERE products.category = 'Food'
UNION
SELECT products.id, products.category, toys.product_name, toys.price, stock.quantity
FROM products
LEFT JOIN toys ON products.id = toys.product_id
LEFT JOIN stock ON toys.product_id = stock.item_id
WHERE products.category = 'Toys'
UNION
SELECT products.id, products.category, clothes.product_name, clothes.price, stock.quantity
FROM products
LEFT JOIN clothes ON products.id = clothes.product_id
LEFT JOIN stock ON clothes.product_id = stock.item_id
WHERE products.category = 'Clothes'";
$result = $conn->query($sql);
while ($row = mysqli_fetch_array($result)) {
$product_name = isset($row['product_name']) ? $row['product_name'] : '';
$quantity = isset($row['quantity']) ? $row['quantity'] : '';
$price = isset($row['price']) ? $row['price'] : '';
echo "<tr>";
echo "<form name='update' action='update_stock.php' method='post'>";
echo "<td><input type='text' name='product_name' value='".$row ['product_name']."'></td>";
echo "<td><input type='text' class='stock--update--num' name='quantity' value='".$row['quantity']."'></td>";
echo "<td><input type='text' class='stock--update--num' name='price' value='".$row['price']. "€"."'></td>";
echo "<td><input type='submit' name='update' value='Update'></td>";
echo "</form>";
echo "</tr>";
}
?>
</table>`
I wanted for it to display each item only once with the correct quantity and price.
Other code I tried:
`$conn = mysqli_connect("localhost:3307", "root", "", "db_login");
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT DISTINCT products.*, hygiene.product_id, hygiene.product_name, hygiene.price, hygiene.image_path, stock.quantity
FROM products
LEFT JOIN hygiene ON products.id = hygiene.product_id
LEFT JOIN stock ON hygiene.product_id = stock.item_id
WHERE products.category = 'Hygiene'
UNION
SELECT DISTINCT products.*, food.product_id, food.product_name, food.price, food.image_path, stock.quantity
FROM products
LEFT JOIN food ON products.id = food.product_id
LEFT JOIN stock ON food.product_id = stock.item_id
WHERE products.category = 'Food'
UNION
SELECT DISTINCT products.*, toys.product_id, toys.product_name, toys.price, toys.image_path, stock.quantity
FROM products
LEFT JOIN toys ON products.id = toys.product_id
LEFT JOIN stock ON toys.product_id = stock.item_id
WHERE products.category = 'Toys'
UNION
SELECT DISTINCT products.*, clothes.product_id, clothes.product_name, clothes.price, clothes.image_path, stock.quantity
FROM products
LEFT JOIN clothes ON products.id = clothes.product_id
LEFT JOIN stock ON clothes.product_id = stock.item_id
WHERE products.category = 'Clothes'";
$result = $conn->query($sql);
while ($row = mysqli_fetch_array($result)) {
echo "<tr>";
echo "<form name='update' action='update_stock.php' method='post'>";
$product_name = isset($row['product_name']) ? $row['product_name'] : '';
$quantity = isset($row['quantity']) ? $row['quantity'] : '';
$price = isset($row['price']) ? $row['price'] : '';
echo "<td><input type='text' name='product_name' value='".$product_name."'></td>";
echo "<td><input type='text' class='stock--update--num' name='quantity' value='".$quantity."'></td>";
echo "<td><input type='text' class='stock--update--num' name='price' value='".$price. "€"."'></td>";
echo "<td><input type='submit' name='update' value='Update'></td>";
echo "</form>";
echo "</tr>";
}`

Answer 1

Wrap all your UNION queries in one single DISTINCT query:
SELECT DISTINCT * FROM(
SELECT...
UNION
SELECT....
UNION
SELECT...
)
But looking at your query closely, you are querying for more columns than you are fetching - I don't think product_ids would make a unique result.