HAVING 子句
在 SQL 中增加 HAVING 子句原因是,WHERE 關鍵字無法與合計函數一起使用。
SQL HAVING 語法
SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value
SQL HAVING 實例
(1)單列分組
我們擁有下面這個 "Orders" 表:
O_Id | OrderDate | OrderPrice | Customer |
---|---|---|---|
1 | 2008/12/29 | 1000 | Bush |
2 | 2008/11/23 | 1600 | Carter |
3 | 2008/10/05 | 700 | Bush |
4 | 2008/09/28 | 300 | Bush |
5 | 2008/08/06 | 2000 | Adams |
6 | 2008/07/21 | 100 | Carter |
現在,我們希望查找訂單總金額少於 2000 的客戶。
我們使用如下 SQL 語句:
SELECT Customer,SUM(OrderPrice) FROM Orders GROUP BY Customer HAVING SUM(OrderPrice)<2000
結果集類似:
Customer | SUM(OrderPrice) |
---|---|
Carter | 1700 |
現在我們希望查找客戶 "Bush" 或 "Adams" 擁有超過 1500 的訂單總金額。
我們在 SQL 語句中增加了一個普通的 WHERE 子句:
SELECT Customer,SUM(OrderPrice) FROM Orders WHERE Customer='Bush' OR Customer='Adams' GROUP BY Customer HAVING SUM(OrderPrice)>1500
結果集:
Customer | SUM(OrderPrice) |
---|---|
Bush | 2000 |
Adams | 2000 |
(2)多列分組
-- 顯示每個部門、每種崗位的平均工資和最高工資
Select deptno,job,avg(sal),max(sal) from emp group by deptno,job;
-- 注意: deptno 和 job 完全相同才顯示一條記錄。
order by
-- 使用 order by 語句 ,desc 是降序排列, asc 是升序排列 , 默認爲升序排列
select * from student_1 order by age desc;
select * from student_1 order by age sname desc; 先按 age 排列,相同的 age 再按 sname 排列