MySQL 表 1 中每个唯一年份的重复行表 2

Question

我需要进行 select 查询来复制表supervisor中每个唯一年份的每个user行。

我目前的查询是：

SELECT 
  a.year, CONCAT(x.first) AS Employee
FROM userdata.users x
LEFT JOIN userdata.supervisor a ON x.userid = a.employeeid
GROUP BY a.year, Employee
ORDER BY x.first, x.last

这给了我 output：

YEAR | EMPLOYEE
2020   Adam
2021   Adam
       Anna
2021   Danielle
2020   John
2021   John

预期 Output：

YEAR | EMPLOYEE
2020   Adam
2021   Adam
2020   Anna
2021   Anna
2020   Danielle
2021   Danielle
2020   John
2021   John

Answer 1

A simple cross join may do.

DROP TABLE IF EXISTS T,T1;

CREATE TABLE T(NAME VARCHAR(10));
CREATE TABLE T1 (YR INT);

INSERT INTO T VALUES ('AAA'),('BBB'),('CCC');
INSERT INTO T1 VALUES (2001),(2002),(2002),(2003),(2004);

SELECT YR,NAME
FROM T USERS
CROSS JOIN (SELECT DISTINCT YR FROM T1) SUPERVISOR
ORDER BY YR,NAME ;

+------+------+
| YR   | NAME |
+------+------+
| 2001 | AAA  |
| 2001 | BBB  |
| 2001 | CCC  |
| 2002 | AAA  |
| 2002 | BBB  |
| 2002 | CCC  |
| 2003 | AAA  |
| 2003 | BBB  |
| 2003 | CCC  |
| 2004 | AAA  |
| 2004 | BBB  |
| 2004 | CCC  |
+------+------+
12 rows in set (0.001 sec)