if语句的mysql语法问题

我对if语句附近的这个语法有问题，我一直在 检查附近的mysql语法

== 'purp1' and product_price==53, 13, 0) as ShipWeight  

这就是我正在努力实现的目标。有什么想法吗

select wp_cart66_order_items.order_id as Order_ID,
   wp_cart66_orders.trans_id as Order_Number,
   wp_cart66_orders.bill_first_name as Bill_First_Name,   
   wp_cart66_orders.bill_last_name as Bill_Last_Name,
   wp_cart66_orders.ship_first_name as Ship_First_Name,
   wp_cart66_orders.ship_last_name as Ship_Last_Name,
   wp_cart66_orders.ship_address as Ship_Address1,
   wp_cart66_orders.ship_address2 as Ship_Address2,
   wp_cart66_orders.ship_city as Ship_City,
   wp_cart66_orders.ship_state as Ship_State,
   wp_cart66_orders.ship_zip as Ship_zip,
   wp_cart66_order_items.item_number as Item_Number,
   wp_cart66_order_items.product_price as Price,
   wp_cart66_order_items.Description as OrderItemsDescription,
if(item_number == 'purp1' and product_price==53, 13, 0) as ShipWeight
from wp_cart66_orders 
inner join wp_cart66_order_items
    on wp_cart66_orders.id=wp_cart66_order_items.order_id 
where wp_cart66_orders.ordered_on between "2013-04-01 00:00:00" and "2013-04-02 23:59:59"

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在浏览文档时，我找不到mysql是否支持

=

，请尝试将其更改为

=

if(item_number = 'purp1' and product_price=53, 13, 0) as ShipWeight

更新1

使用

CASE（）

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删除double==非常好，但是我现在遇到了另一个问题，当我添加另一行时，我得到了两个Shipweight列，如何添加多行而不得到所有这些列？'if（item_number='marley1'和product_price='12.00'，2，0）作为Shipweight，if（item_number='samp1'和product_price='19.50'，4，0）作为ShipWeight'你的意思是结合这两个？如果我有多个产品具有相同的价格，我如何将它们添加到一行，这样我就不会有一个巨大的脚本？我要用逗号把它们分开吗？”当项目编号为“hell1，cav1，marley1”且产品价格为“15.00”时，则2“太好了，非常感谢，非常感谢！！

CASE 
    WHEN item_number = 'marley1' and product_price='12.00' THEN 2
    WHEN item_number = 'samp1' and product_price='19.50' THEN 4
    ELSE 0
END ShipWeight