1364.(Medium)顾客的可信联系人数量
顾客表：Customers
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| customer_id | int |
| customer_name | varchar |
| email | varchar |
+---------------+---------+
customer_id 是这张表的主键。
此表的每一行包含了某在线商店顾客的姓名和电子邮件。联系方式表：Contacts
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| user_id | id |
| contact_name | varchar |
| contact_email | varchar |
+---------------+---------+
(user_id, contact_email) 是这张表的主键。
此表的每一行表示编号为 user_id 的顾客的某位联系人的姓名和电子邮件。
此表包含每位顾客的联系人信息，但顾客的联系人不一定存在于顾客表中。发票表：Invoices
+--------------+---------+
| Column Name | Type |
+--------------+---------+
| invoice_id | int |
| price | int |
| user_id | int |
+--------------+---------+
invoice_id 是这张表的主键。
此表的每一行分别表示编号为 user_id 的顾客拥有有一张编号为 invoice_id、价格为 price 的发票。为每张发票 invoice_id 编写一个SQL查询以查找以下内容：
customer_name：与发票相关的顾客名称。 price：发票的价格。 contacts_cnt：该顾客的联系人数量。 trusted_contacts_cnt：可信联系人的数量：既是该顾客的联系人又是商店顾客的联系人数量（即：可信联系人的电子邮件存在于客户表中）。 将查询的结果按照 invoice_id 排序。
查询结果的格式如下例所示：
Customers table:
+-------------+---------------+--------------------+
| customer_id | customer_name | email |
+-------------+---------------+--------------------+
| 1 | Alice | alice@leetcode.com |
| 2 | Bob | bob@leetcode.com |
| 13 | John | john@leetcode.com |
| 6 | Alex | alex@leetcode.com |
+-------------+---------------+--------------------+
Contacts table:
+-------------+--------------+--------------------+
| user_id | contact_name | contact_email |
+-------------+--------------+--------------------+
| 1 | Bob | bob@leetcode.com |
| 1 | John | john@leetcode.com |
| 1 | Jal | jal@leetcode.com |
| 2 | Omar | omar@leetcode.com |
| 2 | Meir | meir@leetcode.com |
| 6 | Alice | alice@leetcode.com |
+-------------+--------------+--------------------+
Invoices table:
+------------+-------+---------+
| invoice_id | price | user_id |
+------------+-------+---------+
| 77 | 100 | 1 |
| 88 | 200 | 1 |
| 99 | 300 | 2 |
| 66 | 400 | 2 |
| 55 | 500 | 13 |
| 44 | 60 | 6 |
+------------+-------+---------+
Result table:
+------------+---------------+-------+--------------+----------------------+
| invoice_id | customer_name | price | contacts_cnt | trusted_contacts_cnt |
+------------+---------------+-------+--------------+----------------------+
| 44 | Alex | 60 | 1 | 1 |
| 55 | John | 500 | 0 | 0 |
| 66 | Bob | 400 | 2 | 0 |
| 77 | Alice | 100 | 3 | 2 |
| 88 | Alice | 200 | 3 | 2 |
| 99 | Bob | 300 | 2 | 0 |
+------------+---------------+-------+--------------+----------------------+
Alice 有三位联系人，其中两位(Bob 和 John)是可信联系人。
Bob 有两位联系人, 他们中的任何一位都不是可信联系人。
Alex 只有一位联系人(Alice)，并是一位可信联系人。
John 没有任何联系人。来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/number-of-trusted-contacts-of-a-customer
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Solution
Invoices left join Customers left join Contacts
SELECT invoice_id,
max(cus.customer_name) customer_name,
max(price) price,
count(DISTINCT con.contact_email) contacts_cnt,
IFNULL(sum(con.contact_email in (SELECT email FROM Customers)),0) trusted_contacts_cnt
from Invoices i left JOIN
Customers cus on i.user_id = cus.customer_id LEFT JOIN
Contacts con on i.user_id = con.user_id
GROUP BY invoice_id;Table Schema
Create table If Not Exists Customers (customer_id int, customer_name varchar(20), email varchar(30));
Create table If Not Exists Contacts (user_id int, contact_name varchar(20), contact_email varchar(30));
Create table If Not Exists Invoices (invoice_id int, price int, user_id int);
Truncate table Customers;
insert into Customers (customer_id, customer_name, email) values ('1', 'Alice', 'alice@leetcode.com');
insert into Customers (customer_id, customer_name, email) values ('2', 'Bob', 'bob@leetcode.com');
insert into Customers (customer_id, customer_name, email) values ('13', 'John', 'john@leetcode.com');
insert into Customers (customer_id, customer_name, email) values ('6', 'Alex', 'alex@leetcode.com');
Truncate table Contacts;
insert into Contacts (user_id, contact_name, contact_email) values ('1', 'Bob', 'bob@leetcode.com');
insert into Contacts (user_id, contact_name, contact_email) values ('1', 'John', 'john@leetcode.com');
insert into Contacts (user_id, contact_name, contact_email) values ('1', 'Jal', 'jal@leetcode.com');
insert into Contacts (user_id, contact_name, contact_email) values ('2', 'Omar', 'omar@leetcode.com');
insert into Contacts (user_id, contact_name, contact_email) values ('2', 'Meir', 'meir@leetcode.com');
insert into Contacts (user_id, contact_name, contact_email) values ('6', 'Alice', 'alice@leetcode.com');
Truncate table Invoices;
insert into Invoices (invoice_id, price, user_id) values ('77', '100', '1');
insert into Invoices (invoice_id, price, user_id) values ('88', '200', '1');
insert into Invoices (invoice_id, price, user_id) values ('99', '300', '2');
insert into Invoices (invoice_id, price, user_id) values ('66', '400', '2');
insert into Invoices (invoice_id, price, user_id) values ('55', '500', '13');
insert into Invoices (invoice_id, price, user_id) values ('44', '60', '6');Last updated