SQL HAVING 子句

　在 SQL 中增加 HAVING 子句原因是，WHERE 關(guān)鍵字無法與 Aggregate 函數(shù)一起使用。

　HAVING子句已添加到SQL中，因?yàn)閃HERE關(guān)鍵字不能用于聚合函數(shù)。

SQL HAVING 語法

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

演示數(shù)據(jù)庫

　以下是羅斯文示例數(shù)據(jù)庫中"Customers"表的選擇：

CustomerID CustomerName ContactName Address City PostalCode Country
1

Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4

Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbk?p Christina Berglund Berguvsv?gen 8 Lule? S-958 22 Sweden

SQL HAVING示例

　以下SQL語句列出了每個(gè)國家/地區(qū)的客戶數(shù)量。只包括超過5位客戶的國家/地區(qū)：

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

　以下SQL語句列出每個(gè)國家的客戶數(shù)量，從高到低排序（僅包括擁有超過5名客戶的國家/地區(qū)）：

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


演示數(shù)據(jù)庫

　以下是羅斯文示例數(shù)據(jù)庫中"Orders"表的一個(gè)選擇：

OrderID CustomerID EmployeeID OrderDate ShipperID
10248 90 5 1996-07-04 3
10249 81 6 1996-07-05 1
10250 34 4 1996-07-08 2

并從"Employees"表中選擇：

EmployeeID LastName FirstName BirthDate Photo Notes
1 Davolio Nancy 1968-12-08 EmpID1.pic Education includes a BA....
2 Fuller Andrew 1952-02-19 EmpID2.pic Andrew received his BTS....
3 Leverling Janet 1963-08-30 EmpID3.pic Janet has a BS degree....

更多HAVING示例

　以下SQL語句列出已注冊超過10個(gè)訂單的員工：

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語句列出員工“Davolio”或“Fuller”是否已注冊超過25個(gè)訂單：

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;