如何在SQL Server中使用CASE和2表

Question

我有两个数据表成员和交易

样品：

成员

Members_Id | Name |  Adress  |rental_amount |
---------------------------------------------
    A01    | John | New York |     4        |
    A02    | Mark | German   |     2        |
    A03    | Ika  | France   |     5        |

交易

NumberTransac |Number_plate|  Discount|  Price  |Members_Id |
---------------------------------------------------------------
      1       | AA8866DG   |     0    | $90000  |   A01     |
      2       | AB5536HG   |     0    | $8000   |   A01     |
      3       | BG7677HJ   |     0    | $70000  |   A03     |

我想计算字段rental_amount和折扣 使用CASE

如果租金数量> 3然后字段“Discount”将被添加'100000'

IF  (SELECT COUNT(*) FROM Members.rental_amount WHERE ) > 3 INSERT INTO     Transaction(Discount) VALUES ('100000') ELSE INSERT INTO Transaction(Discount) VALUES ('100000') ; GO

我仍然感到困惑，如果sql中的设备如果...请帮帮我..谢谢

Answer 1

使用UPDATE声明：

UPDATE transaction
SET discount = 100000
WHERE Members_Id IN
   (SELECT Members_Id
    FROM members 
    WHERE rental_amount > 3 )