LeetCode-1303. Team size

The employee table ：Employee

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| employee_id   | int     |
| team_id       | int     |
+---------------+---------+
employee_id The field is the primary key of this table , Each row in the table contains the for each employee ID And their team .
Write a SQL Inquire about , To find the total number of people in each employee's team .

There are no specific requirements for the order in the query results .

An example of query result format is as follows ：

Employee Table:
+-------------+------------+
| employee_id | team_id    |
+-------------+------------+
|     1       |     8      |
|     2       |     8      |
|     3       |     8      |
|     4       |     7      |
|     5       |     9      |
|     6       |     9      |
+-------------+------------+
Result table:
+-------------+------------+
| employee_id | team_size  |
+-------------+------------+
|     1       |     3      |
|     2       |     3      |
|     3       |     3      |
|     4       |     1      |
|     5       |     2      |
|     6       |     2      |
+-------------+------------+
ID by 1、2、3 Our employees are team_id by 8 Members of our team ,
ID by 4 Our employees are team_id by 7 Members of our team ,
ID by 5、6 Our employees are team_id by 9 Members of our team .

# Write your MySQL query statement below
#  Parent query left connection , Being a father team_id With son team_id Equal is enough 
SELECT e1.employee_id, e2.team_size  FROM Employee AS e1 LEFT JOIN
(
#  The subquery first finds each team_id Of team_size
SELECT team_id AS tmp_id, COUNT(team_id) AS team_size FROM Employee 
GROUP BY team_id
) AS e2 ON e1.team_id = e2.tmp_id;