1421. 净现值查询

SQL架构

表: NPV

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| year          | int     |
| npv           | int     |
+---------------+---------+
(id, year) 是该表主键.
该表有每一笔存货的年份, id 和对应净现值的信息.

表: Queries

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| year          | int     |
+---------------+---------+
(id, year) 是该表主键.
该表有每一次查询所对应存货的 id 和年份的信息.

写一个 SQL, 找到 Queries 表中每一次查询的净现值.

结果表没有顺序要求.

查询结果的格式如下所示:

NPV 表:
+------+--------+--------+
| id   | year   | npv    |
+------+--------+--------+
| 1    | 2018   | 100    |
| 7    | 2020   | 30     |
| 13   | 2019   | 40     |
| 1    | 2019   | 113    |
| 2    | 2008   | 121    |
| 3    | 2009   | 12     |
| 11   | 2020   | 99     |
| 7    | 2019   | 0      |
+------+--------+--------+

Queries 表:
+------+--------+
| id   | year   |
+------+--------+
| 1    | 2019   |
| 2    | 2008   |
| 3    | 2009   |
| 7    | 2018   |
| 7    | 2019   |
| 7    | 2020   |
| 13   | 2019   |
+------+--------+

结果表:
+------+--------+--------+
| id   | year   | npv    |
+------+--------+--------+
| 1    | 2019   | 113    |
| 2    | 2008   | 121    |
| 3    | 2009   | 12     |
| 7    | 2018   | 0      |
| 7    | 2019   | 0      |
| 7    | 2020   | 30     |
| 13   | 2019   | 40     |
+------+--------+--------+

(7, 2018)的净现值不在 NPV 表中, 我们把它看作是 0.
所有其它查询的净现值都能在 NPV 表中找到.

用 on ...:

# Write your MySQL query statement below
select
q.id,q.year,ifnull(n.npv,0) npv
from
Queries q left join NPV n
on
q.id = n.id and q.year = n.year

用 using():

select
q.id,q.year,ifnull(n.npv,0) npv
from
Queries q left join NPV n
using(id,year)

select
q.id,q.year,ifnull(n.npv,0) npv
from
Queries q left join NPV n
on
q.id = n.id and q.year = n.year