Mysql SQL选择至少有2个订单的员工,其中至少一个订单位于某个地区,没有嵌套的SQL块
我有两个表,“客户”和“员工”,它们在第三个表“订单”中连接起来Mysql SQL选择至少有2个订单的员工,其中至少一个订单位于某个地区,没有嵌套的SQL块,mysql,sql,Mysql,Sql,我有两个表,“客户”和“员工”,它们在第三个表“订单”中连接起来 | CustomerID | CDistrict | | EmployeeID | EName | |------------|-----------| |------------|-------| | 1 | A | | 1 | Alex | | 2 | A | | 2 | Bob | |
| CustomerID | CDistrict | | EmployeeID | EName |
|------------|-----------| |------------|-------|
| 1 | A | | 1 | Alex |
| 2 | A | | 2 | Bob |
| 3 | B | | 3 | Edd |
| 4 | C |
| OrderID | CustomerID | EmployeeID |
|---------|------------|------------|
| 1 | 1 | 1 |
| 2 | 3 | 1 |
| 3 | 3 | 2 |
| 4 | 5 | 2 |
| 5 | 1 | 3 |
我如何选择至少服务过2份订单的所有员工的姓名,其中至少有一份订单是为来自没有嵌套SQL块的地区“a”的客户提供的?也就是说,结果应该是“Alex”我通过嵌套查询实现了这一点,如下所示:
SELECT EName FROM Database.Employees
WHERE
EmployeeID IN
(SELECT EmployeeID FROM Database.Orders
GROUP BY EmployeeID
HAVING COUNT(*) >= 2)
AND
EmployeeID IN
(SELECT EmployeeID FROM Database.Orders
WHERE
CustomerID IN
(SELECT CustomerID FROM Database.Customers
WHERE CDistrict = 'A'));
但是,我需要在不使用嵌套查询的情况下执行此操作。
我的查询用于选择至少服务过2份订单的所有员工,如下所示:
SELECT EName FROM Database.Employees, Database.Orders
WHERE
Employees.EID = Orders.EID
GROUP BY EName HAVING COUNT(OrderID) >=2
ORDER BY EName;
SELECT EName FROM Database.Employees, Database.Orders, Database.Customers
WHERE
Employees.EID = Orders.EID
AND
Orders.CID = Customers.CID
AND
CDistrict = 'A';
我的查询用于选择从地区“a”为客户提供服务的所有员工,如下所示:
SELECT EName FROM Database.Employees, Database.Orders
WHERE
Employees.EID = Orders.EID
GROUP BY EName HAVING COUNT(OrderID) >=2
ORDER BY EName;
SELECT EName FROM Database.Employees, Database.Orders, Database.Customers
WHERE
Employees.EID = Orders.EID
AND
Orders.CID = Customers.CID
AND
CDistrict = 'A';
但是,当我尝试将这些查询连接到单个查询时,如
SELECT EName FROM Database.Employee, Database.Orders, Database.Customers
WHERE
Employees.EID = Orders.EID
AND
Orders.CID = Customers.CID
AND
CDistrict = 'A'
GROUP BY EName HAVING COUNT(OrderID) >=2;
结果我变成了0。我想,这个查询可能会搜索在“A”区至少服务过2份订单的所有员工,但这不是我需要的-我需要至少服务过两份订单的员工,其中至少一份在“A”区。我做错了什么?如何将嵌套查询转换为常规查询?使用
groupby
和HAVING
:
SELECT o.EmployeeID
FROM Database.Orders o JOIN
Database.Customers c
ON o.CustomerId = c.CustomerId
GROUP BY o.EmployeeID
HAVING COUNT(*) >= 2 AND
SUM(c.CDistrict = 'A') > 0;
这几乎奏效,但我需要的是员工的姓名,而不是员工的姓名ID@ZyTelevan . . . 您应该能够返回到
Employees
表以获取姓名(记住将姓名包括在分组中)。