mysql - 插入一对一关系

Question

我的 MySQL 数据库包含两个表:user 和 coupon(一对一关系)。

我想选择所有没有优惠券的用户并创建一个新的(随机且唯一的)。

user TABLE:
___________________________________
|  id   |   name   |   coupon_id  |
-----------------------------------
   1        John         5
   2        Mary         (null)  // Need to create one coupon.
   3        Doe          2
   4        Max          (null)  // Need to create one coupon.
   5        Rex          1
   7        Bill         (null)  // Need to create one coupon.


coupon TABLE:
______________________________________________
|  id   |   code (random 6-chars - unique)   |
----------------------------------------------
   1        80k2ni
   2        0akdne
   5        nk03jd

---

快捷方式:

选择所有没有优惠券的用户:SELECT * from user WHERE coupon_id IS NULL;

生成一个随机的 6 个字符的字符串 (MySQL):LEFT(sha1(rand()), 6)。

Answer 1

假设您不介意从 6 继续向上获取下一个 coupon_id，这可以按如下方式完成(参见 SQL Fiddle Demo):

-- Declare and set variables
SET @id_for_insert = (SELECT MAX(`id`) FROM `coupon`);
SET @id_for_update = @id_for_insert;

-- Insert new coupons
INSERT INTO `coupon` (id, code)
SELECT @id_for_insert := @id_for_insert + 1, LEFT(SHA1(RAND()), 6)
FROM `user`
WHERE coupon_id IS NULL;

-- Update users that don't already have a coupon with the newly created coupons
UPDATE `user`
SET coupon_id = @id_for_update := @id_for_update + 1
WHERE coupon_id IS NULL;