添加优惠券功能，实现价格计算

scripts/sql/init.sql

@@ -819,4 +819,40 @@ comment on column bill.created_at is '创建时间';
 comment on column bill.updated_at is '更新时间';
 comment on column bill.deleted_at is '删除时间';
 
+-- coupon 优惠券
+drop table if exists coupon cascade;
+create table coupon (
+    id          serial primary key,
+    user_id     int references "user" (id)
+        on update cascade
+        on delete cascade,
+    code        varchar(255)   not null unique,
+    remark      varchar(255),
+    amount      decimal(12, 2) not null default 0,
+    min_amount decimal(12, 2) not null default 0,
+    status      int            not null default 0,
+    expire_at   timestamp,
+    created_at  timestamp               default current_timestamp,
+    updated_at  timestamp               default current_timestamp,
+    deleted_at  timestamp
+);
+create index coupon_user_id_index on coupon (user_id);
+create index coupon_code_index on coupon (code);
+create index coupon_status_index on coupon (status);
+create index coupon_deleted_at_index on coupon (deleted_at);
+
+-- coupon表字段注释
+comment on table coupon is '优惠券表';
+comment on column coupon.id is '优惠券ID';
+comment on column coupon.user_id is '用户ID';
+comment on column coupon.code is '优惠券代码';
+comment on column coupon.remark is '优惠券备注';
+comment on column coupon.amount is '优惠券金额';
+comment on column coupon.min_amount is '最低消费金额';
+comment on column coupon.status is '优惠券状态：0-未使用，1-已使用，2-已过期';
+comment on column coupon.expire_at is '过期时间';
+comment on column coupon.created_at is '创建时间';
+comment on column coupon.updated_at is '更新时间';
+comment on column coupon.deleted_at is '删除时间';
+
 -- endregion