Mysql Code to Sqlite Code

I have a project in MySQL/PHP (YII) I have a code in mysql I want a code convert into sqlite .I have not much knowledge of sqlite any help should be appreciated .

SELECT  sum(Orders.total) as total FROM Orders
    where 
    IF(Orders.merge_split = "merge",Orders.merge_split_ids =:oid  , Orders.id =:oid)
    and Orders.admin_id=:admin

    UNION

    SELECT CAST(sum(Cashier_discount.discount) as DECIMAL(10,2)) as cashier_discount from Cashier_discount
    where Cashier_discount.order_id=:oid and Cashier_discount.admin_id=:admin