Query Profit Sales

SELECT
    (
        -- Calculate profit from sales
        COALESCE(SUM(tbl_sales_product.subtotal), 0)
        - COALESCE(SUM(tbl_sales_product.cost_price * tbl_sales_product.quantity), 0)
    )
    -
    (
        -- Subtract returns
        COALESCE(SUM(tbl_returns_product.subtotal), 0)
        + COALESCE(SUM(tbl_returns_product.cost_price * tbl_returns_product.quantity), 0)
    )
    -
    (
        -- Remove VAT from sales
        COALESCE(SUM(
            CASE
                WHEN tbl_sales_product.total_tax_val = 0 THEN 0
                WHEN tbl_sales_product.second_hand = 1 THEN
                    (tbl_sales_product.subtotal - tbl_sales_product.cost_price)
                    - ((tbl_sales_product.subtotal - tbl_sales_product.cost_price) / 1.23)
                ELSE
                    tbl_sales_product.subtotal - (tbl_sales_product.subtotal / 1.23)
            END
        ), 0)
    )
    +
    (
        -- Add VAT from credit notes
        COALESCE(SUM(
            CASE
                WHEN tbl_returns_product.total_tax_val = 0 THEN 0
                WHEN tbl_returns_product.second_hand = 1 THEN
                    (tbl_returns_product.subtotal - tbl_returns_product.cost_price)
                    - ((tbl_returns_product.subtotal - tbl_returns_product.cost_price) / 1.23)
                ELSE
                    tbl_returns_product.subtotal - (tbl_returns_product.subtotal / 1.23)
            END
        ), 0)
    ) AS final_profit
FROM
    isellpt_isystem_new.tbl_sales_product AS tbl_sales_product
    LEFT JOIN isellpt_isystem_new.tbl_returns_product AS tbl_returns_product ON 1 = 1