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语句用法

  • 2020-03-05 20:17
  • 数据库知识
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研商函数 (举例 SUMState of Qatar 常常供给增加 GROUP BY 语句。GROUP BY 语句GROUP BY 语句用于结合合计函数,依据二个或多少个列对结果集进行分组。

SQL GROUP BY 语法SELECT column_name, aggregate_function(column_name)FROM table_nameWHERE column_name operator valueGROUP BY column_nameSQL GROUP BY 实例大家有着下边这些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

当今,大家期待物色每一个客商的总金额。

大家想要使用 GROUP BY 语句对客商实行整合。

大家利用下列 SQL 语句:

SELECT Customer,SUM(OrderPrice卡塔尔(قطر‎ FROM OrdersGROUP BY Customer结果集相近那样:

Customer SUM(OrderPrice) Bush 2000 Carter 1700 Adams 2000

很棒吧,对不对?

让大家看一下即便省略 GROUP BY 会现身什么情状:

SELECT Customer,SUM(Order普赖斯State of Qatar FROM Orders结果集相近那样:

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

地点的结果集不是大家需求的。

那么为何不可能应用方面那条 SELECT 语句呢?解释如下:下边包车型地铁 SELECT 语句内定了两列。SUM(OrderPrice卡塔尔 重临三个独立的值,而 Customer 重返 6 个值。由此,大家得不到准确的结果。不过,您已经观望了,GROUP BY 语句解决了那几个主题素材。GROUP BY 叁个之上的列大家也得以对三个之上的列应用 GROUP BY 语句,如同这么:

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

综述实例

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

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