SQL语法——SQL HAVING 语法

HAVING 子句能够指定过滤条件，从而控制查询结果中哪些组可以出现在最终结果里面。

WHERE 子句对被选择的列施加条件，而 HAVING 子句则对 GROUP BY 子句所产生的组施加条件。

SQL HAVING 语法:

SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
HAVING condition
ORDER BY column_name(s);

在 SELECT 查询中，HAVING 子句必须紧随 GROUP BY 子句，并出现在 ORDER BY 子句（如果有的话）之前。

SQL HAVING示例

以下SQL语句列出了每个国家/地区的客户数量。只包括超过5位客户的国家/地区：

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
HAVING COUNT(CustomerID) > 5;

以下SQL语句列出每个国家的客户数量，从高到低排序（仅包括拥有超过5名客户的国家/地区）：

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
HAVING COUNT(CustomerID) > 5
ORDER BY COUNT(CustomerID) DESC;

以下SQL语句列出已注册超过10个订单的员工：

SELECT Employees.LastName, COUNT(Orders.OrderID) AS NumberOfOrders
FROM Orders
INNER JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID)
GROUP BY LastName
HAVING COUNT(Orders.OrderID) > 10;

以下SQL语句列出员工“Davolio”或“Fuller”是否已注册超过25个订单：

SELECT Employees.LastName, COUNT(Orders.OrderID) AS NumberOfOrders
FROM Orders
INNER JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID
WHERE LastName = 'Davolio' OR LastName = 'Fuller'
GROUP BY LastName
HAVING COUNT(Orders.OrderID) > 25;