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sql group by 语句用法

让我们看一下如果省略 GROUP BY 会出现什么情况:

很棒吧,对不对?

上面的结果集不是我们需要的。

Customer SUM(OrderPrice) Bush 5700 Carter 5700 Bush 5700 Bush 5700 Adams 5700 Carter 5700

综合实例

create table employee(2 ID int,3 name nvarchar (10),4 salary int,5 start_date datetime,6 city nvarchar (10),7 region char (1))8 GO12 insert into employee (ID, name, salary, start_date, city, region)3 values (1, 'Jason', 40420, '02/01/94', 'New York', 'W')4 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (2, 'Robert',14420, '01/02/95', 'Vancouver','N')3 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (3, 'Celia', 24020, '12/03/96', 'Toronto', 'W')3 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (4, 'Linda', 40620, '11/04/97', 'New York', 'N')3 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (5, 'David', 80026, '10/05/98', 'Vancouver','W')3 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (6, 'James', 70060, '09/06/99', 'Toronto', 'N')3 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (7, 'Alison',90620, '08/07/00', 'New York', 'W')3 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (8, 'Chris', 26020, '07/08/01', 'Vancouver','N')3 GO

(1 rows affected)1 insert into employee (ID, name, salary, start_date, city, region)2 values (9, 'Mary', 60020, '06/09/02', 'Toronto', 'W')3 GO

(1 rows affected)12 select * from employee3 GOID name salary start_date city region----------- ---------- ----------- ----------------------- ---------- ------ 1 Jason 40420 1994-02-01 00:00:00.000 New York W 2 Robert 14420 1995-01-02 00:00:00.000 Vancouver N 3 Celia 24020 1996-12-03 00:00:00.000 Toronto W 4 Linda 40620 1997-11-04 00:00:00.000 New York N 5 David 80026 1998-10-05 00:00:00.000 Vancouver W 6 James 70060 1999-09-06 00:00:00.000 Toronto N 7 Alison 90620 2000-08-07 00:00:00.000 New York W 8 Chris 26020 2001-07-08 00:00:00.000 Vancouver N 9 Mary 60020 2002-06-09 00:00:00.000 Toronto W

(9 rows affected)12 --GROUP BY clause with an aggregator 'SUM()'.34 SELECT region, SUM(Salary)5 FROM Employee6 WHERE ID BETWEEN 1 AND 107 GROUP BY Region8 GOregion------ -----------N 151120W 295106

(2 rows affected)123 drop table employee4 GO1

SELECT Customer,SUM(OrderPrice) FROM OrdersGROUP BY Customer结果集类似这样:

我们想要使用 GROUP BY 语句对客户进行组合。

SQL GROUP BY 语法SELECT column_name, aggregate_function(column_name)FROM table_nameWHERE column_name operator valueGROUP BY column_nameSQL GROUP BY 实例我们拥有下面这个 Orders 表:

我们使用下列 SQL 语句:

那么为什么不能使用上面这条 SELECT 语句呢?解释如下:上面的 SELECT 语句指定了两列。SUM(OrderPrice) 返回一个单独的值,而 Customer 返回 6 个值。因此,我们得不到正确的结果。不过,您已经看到了,GROUP BY 语句解决了这个问题。GROUP BY 一个以上的列我们也可以对一个以上的列应用 GROUP BY 语句,就像这样:

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

SELECT Customer,SUM(OrderPrice) FROM Orders结果集类似这样:

Customer SUM(OrderPrice) Bush 2000 Carter 1700 Adams 2000

现在,我们希望查找每个客户的总金额。

SELECT Customer,OrderDate,SUM(OrderPrice) FROM OrdersGROUP BY Customer,OrderDate

合计函数 (比如 SUM) 常常需要添加 GROUP BY 语句。GROUP BY 语句GROUP BY 语句用于结合合计函数,根据一个或多个列对结果集进行分组。

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