如何在MySQL中进行特定查询

Question

mysql> select * from  Orders;
+------+------+------+------------+------------+
| ONO  | CNO  | ENO  | RECEIVED   | SHIPPED    |
+------+------+------+------------+------------+
| 1020 | 1111 | 1000 | 1994-12-10 | 1994-12-12 |
| 1021 | 1111 | 1000 | 1995-01-12 | 1995-01-15 |
| 1022 | 2222 | 1001 | 1995-02-13 | 1995-02-20 |
| 1023 | 3333 | 1000 | 2003-02-15 | NULL       |
| 1024 | 4444 | 1000 | 2003-02-15 | 2003-02-16 |
| 1025 | 5555 | 1000 | 2003-02-15 | 2003-02-16 |
+------+------+------+------------+------------+

mysql> select * from Employees;
+------+--------+-------+------------+
| ENO  | ENAME  | ZIP   | HDATE      |
+------+--------+-------+------------+
| 1000 | Jones  | 67226 | 1995-12-12 |
| 1001 | Smith  | 60606 | 1992-01-01 |
| 1002 | Brown  | 50302 | 1994-09-01 |
| 1003 | Green  | 28411 | 2002-09-01 |
| 1004 | Purple | 28411 | 2003-01-01 |
+------+--------+-------+------------+

mysql> select * from Customers;
+------+---------+------------------+-------+--------------+
| CNO  | CNAME   | STREET           | ZIP   | PHONE        |
+------+---------+------------------+-------+--------------+
| 1111 | Charles | 123 Main St.     | 67226 | 316-636-5555 |
| 2222 | Bertram | 237 Ash Avenue   | 67226 | 316-689-5555 |
| 3333 | Barbara | 111 Inwood St.   | 60606 | 316-111-1234 |
| 4444 | Will    | 111 Kenwood St.  | 54444 | 416-111-1234 |
| 5555 | Bill    | 211 Marlwood St. | 28408 | 416-111-1235 |
| 6666 | Keely   | 211 Pinewood St. | 28411 | 416-111-1235 |
| 7777 | Maera   | 211 Marlwood St. | 28408 | 416-111-1235 |
+------+---------+------------------+-------+--------------+

我需要：获取cname和ename对，以使名称为cname的客户通过名称为ename员工下订单。

我敢肯定，这对大多数人来说似乎很容易，但我一直无法弄清楚。 我已经试过了：

select distinct Customers.CNAME, Employees.ENAME
from   Customers, Employees
where  Customers.CNO in (
    select Customers.CNO
    from   Customers, Orders
    where  Customers.CNO = Orders.CNO
) and
where  Employees.ENO in (
    select Employees.ENO
    from   Orders, Employees
    where  Employees.ENO = Orders.ENO
);

有多个版本，但我似乎无法正常使用。 这是我第一次使用SQL，因此对我来说是非常新的。 我真的很感谢您的帮助。

Answer 1

您可以使用带一对连接的select distinc（如果打开条件不匹配，则使用左连接；如果匹配，则使用内部连接）

select distinct c.cname, e.ename
from Customers as c
left join Orders as o as o on o.cno = c.cno
left join Employees on e.eno =  o.eno

select distinct c.cname, e.ename
from Customers as c
inner join Orders as o as o on o.cno = c.cno
inner join Employees on e.eno =  o.eno

Answer 2

select customers.CNAME, employees.ENAME from customers 
inner join orders on customers.CNO = orders.CNO
inner join employees on orders.ENO = employees.ENO;

使用join语句可以更轻松地读取您要执行的SQL。 这会将订单表连接到CNO值上的客户，并将订单表与员工连接到ENO值上。 然后，选择两列进行显示。

Answer 3

尝试这个

 SELECT DISTINCT Customers.CNAME,Employees.ENAME FROM Customers 
 JOIN Orders ON Customers.CNO=Orders.CNO 
 JOIN Employees ON Employees.ENO=Orders.ENO;

要么

 SELECT DISTINCT Customers.CNAME,Employees.ENAME from Customers 
 JOIN Orders USING (CNO) 
 JOIN Employees USING(ENO);

Answer 4

SELECT DISTINCT c.cname, e.ename
  FROM orders o
  JOIN employees e USING (eno)
  JOIN clients c USING (cno);