SELECT DISTINCT 和 GROUP BY 可以一起使用吗？

Question

是否可以同时使用 SELECT DISTINCT 和 GROUP BY 子句？我需要 DISTINCT 来避免重复值并输入记录的单个条目，然后获取这些重复值的总数。

例如，我有像项目名称和数量这样的列，它们的记录是(产品 A,5),(产品 A,7).

由于产品相同，我希望将其作为单个条目然后合计其数量。所以，我报告的输出是这样的：(product A,12)

DISTINCT 和 GROUP BY 子句可以一起解决这个问题吗？

Answer 1

GROUP BY 会产生不同的行，它会自动执行此操作，您不需要 SELECT DISTINCT 来减少行数。

CREATE TABLE mytable(
   product  VARCHAR(1) NOT NULL
  ,quantity INTEGER  NOT NULL
);
INSERT INTO mytable(product,quantity) VALUES ('a',7);
INSERT INTO mytable(product,quantity) VALUES ('a',5);
INSERT INTO mytable(product,quantity) VALUES ('b',17);
INSERT INTO mytable(product,quantity) VALUES ('b',15);

select product, sum(quantity) as qty
from mytable
group by product


product | qty
:------ | --:
a       |  12
b       |  32

db<>fiddle here 请注意，该结果中只有一行，即名为 product 的列中的每个不同值只有一行，因为我们在 GROUP BY 子句中指定了该列。

db<>fiddle here

Answer 2

根据您对 Used_By_Already 的回答的评论，我认为您需要使用 sum() over (...) 构造，例如以下...

create table [dbo].[Purchases_Supplier] (
  [Purchased From] nvarchar(50),
  Address nvarchar(50),
  [Transaction Month] nvarchar(6),
  Category nvarchar(50),
  Articles nvarchar(50),
  Unit int,
  [Unit Price] money,
  Qty int,
  Tin nvarchar(50),
  Cashier nvarchar(50)
);

insert [dbo].[Purchases_Supplier] values
  ('Acme', '123 Street', '202003', 'Baubles', 'Product A', 1, 1.1, 5, 'Nickel', 'John'),
  ('Acme', '123 Street', '202003', 'Baubles', 'Product A', 1, 1.1, 7, 'Nickel', 'John'),
  ('Acme', '123 Street', '202003', 'Baubles', 'Product B', 1, 1.1, 9, 'Silver', 'Maria'),
  ('Acme', '123 Street', '202003', 'Baubles', 'Product B', 1, 1.1, 11, 'Silver', 'Maria');

declare @Supplier_Name nvarchar(50) = N'Acme',
  @Month_Purc nvarchar(6) = '202003',
  @Cat nvarchar(50) = 'Baubles';

select
  Articles,
  Qty,
  Unit,
  [Unit Price],
  [Purchased From],
  Address,
  Tin,
  Cashier,
  -- NOTE: partition by has everything in the GROUP BY except [Qty]...
  sum(Qty) over (partition by Articles, Unit, [Unit Price], [Purchased From], Address, Tin, Cashier) as Total
from dbo.Purchases_Supplier
where [Purchased From] = @Supplier_Name
and [Transaction Month] = @Month_Purc
and Category = @Cat
group by Articles, Qty, Unit, [Unit Price], [Purchased From], Address, Tin, Cashier;

产生结果：

Articles  Qty  Unit  Unit Price  Purchased From  Address     Tin    Cashier  Total
Product A   5     1      1.1000  Acme            123 Street  Nickel John        12
Product A   7     1      1.1000  Acme            123 Street  Nickel John        12
Product B   9     1      1.1000  Acme            123 Street  Silver Maria       20
Product B  11     1      1.1000  Acme            123 Street  Silver Maria       20

SELECT DISTINCT 和 GROUP BY 可以一起使用吗？

Is it possible to use SELECT DISTINCT and GROUP BY together?

sql

sql-server

group-by

distinct