SQL If Else Statement calculate sum total from 3 tables

Novice here so please go easy!

I want to add a markup price to a products (costprice + supplier delivery charge) which will determine the sell price.
The markup will vary dependent on price range, a category or brand surcharge can be added instead of the markup range price

Distributor Table

Stock Table
StockID    |    DistributorID    |    Brand        |    Category    |    SKU        |    CostPrice    |    SellPrice    
——————————————————————————————————————————-
1               |          1                  |    Apple        |    Phone        |    ABC12         |    25.00      |        
2               |          1                  |    Nokia         |    Phone        |    ABC34        |    119.00    |    
3               |          2                  |    Samsung  |    Tablet         |    ABC35        |    242.00    |
4               |          3                  |    Philips       |    TV              |    ABC56        |    333.50    |

Markup Table
ID | Brand   |  Category | DefaultMarkup | MarkupMinPrice | MarkupMaxPrice |MarkupPrice    
————————————————————————————————————————————–
1  |               |   Tablet     |          20             |         0.00              |        9999.99        |     30.00
2  |   Nokia  |                   |          20            |         100.00          |        599.99          |      20.00
3  |               |                   |          20            |          0.00              |       199.99           |      10.00
4  |               |                   |          20            |          200.00         |       299.99           |      15.00
5  |               |                   |          20            |          300.00         |       399.99           |      20.00    

The following will calculate the Stock.SellPrice by adding the Distributor.DeliveryCharge to the Stock.CostPrice

$sql = "Update Stock s INNER JOIN Distributor d on s.DistributorID = d.DistyID SET s.SellPrice = s.CostPrice + d.DeliveryCharge;";

However i need to add the MarkupPrice from the Markup table too.
There may be a surcharge to brand or Category
The markup price will be in a range (Min / Max)

Example

1. Product costprice is 125.00 from DistyID 3 (no brand / category markup),
   it needs to calculate the sum (125.00 costprice +8.00 deliverycharge)+20.00Markup = SellPrice 153.00
2. Product costprice is 452.00 from DistyID 4 (brand Nokia), it needs to calculate (452.00 costprice+5.00 deliverycharge)+20.00NokiaMarkup = 477.00 Sellprice

   Markup prices will be based on priority from the markup table rules
   I’m also unsure how to join the Markup table to the Stock table as theres no relationship

I believe something along the lines below is what i’m looking for if anyone can help?

If  (Stock.CostPrice <= Markup.MarkupMinPrice) && (s.CostPrice <= MarkupMaxPrice) {
// BRAND MARKUP
If {
Stock.Brand = Markup.Brand 
$sql = "Update Stock s INNER JOIN Distributor d on s.DistributorID = d.DistyID SUM (s.CostPrice + d.DeliveryCharge) AS totalcost JOIN MarkupTable m; s.SellPrice = totalcost + m.MarkupPrice;"
}
elseif{
// CATEGORY MARKUP
Stock.Category = Markup.Category
$sql = "Update Stock s INNER JOIN Distributor d on s.DistributorID = d.DistyID SUM (s.CostPrice + d.DeliveryCharge) AS totalcost JOIN MarkupTable m; s.SellPrice = totalcost + m.MarkupPrice;"
}
else{
// STANDARD PRICE MARKUP 
$sql = "Update Stock s INNER JOIN Distributor d on s.DistributorID = d.DistyID SUM (s.CostPrice + d.DeliveryCharge) AS totalcost JOIN MarkupTable m; s.SellPrice = totalcost + m.MarkupPrice;"
}
else{
//USE MARKUP.DEFAULT MARKUP 
$sql = "Update Stock s INNER JOIN Distributor d on s.DistributorID = d.DistyID SUM (s.CostPrice + d.DeliveryCharge) AS totalcost JOIN MarkupTable m; s.SellPrice = totalcost + m.MarkupPrice;"
}

endif;
}

>Solution :

Use multiple LEFT JOIN with the Markup table, matching different columns. Then use COALESCE() to get the markup amounts in priority order.

UPDATE Stock AS s
JOIN Distributor AS d ON s.DistributorID = d.DistyID
LEFT JOIN Markup AS mb ON s.Brand = mb.Brand
LEFT JOIN Markup AS mc ON s.Category = mc.Category
LEFT JOIN Markup AS mp ON s.CostPrice BETWEEN mp.MarkupMinPrice and mp.MarkupMaxPrice
SET s.SellPrice = s.CostPrice + d.DeliveryCharge + COALESCE(mb.MarkupPrice, mc.MarkupPrice, mp.MarkupPrice, 0)