Database daily question - day 20: selling products by date

One 、 Problem description

surface

 

Activities

：

+-------------+---------+
|  Name  |  type  |
+-------------+---------+
| sell_date | date |
| product | varchar |
+-------------+---------+
This table has no primary key , It may contain duplicates .
Each row of this table contains the product name and the date of sale in the market .


Write a  

SQL

  Query to find each

date

、 Selling different products

Quantity and name

. The name of the product sold on each date shall be in accordance with

Dictionary order

array . Back to press  

sell_date

  Sorted result table .

Query results

The format is shown in the following example .

Topic link

：

Sell products by date

Two 、 Subject requirements

Examples

Input ：
Activities  surface ：
+------------+-------------+
| sell_date | product |
+------------+-------------+
| 2020-05-30 | Headphone |
| 2020-06-01 | Pencil |
| 2020-06-02 | Mask |
| 2020-05-30 | Basketball |
| 2020-06-01 | Bible |
| 2020-06-02 | Mask |
| 2020-05-30 | T-Shirt |
+------------+-------------+
Output ：
+------------+----------+------------------------------+
| sell_date | num_sold | products |
+------------+----------+------------------------------+
| 2020-05-30 | 3 | Basketball,Headphone,T-shirt |
| 2020-06-01 | 2 | Bible,Pencil |
| 2020-06-02 | 1 | Mask |
+------------+----------+------------------------------+
explain ：
about 2020-05-30, The items for sale are  (Headphone, Basketball, T-shirt), Arrange in dictionary order , And use commas  ','  Separate .
about 2020-06-01, The items for sale are  (Pencil, Bible), Arrange in dictionary order , Separated by a comma .
about 2020-06-02, The items for sale are  (Mask), Just return the item name .


Investigate

1. Aggregate functions 、 logic analysis
2. It is recommended to use time 10~25min


3、 ... and 、 Problem analysis

This question mainly examines

Aggregate analysis

and

Sorting function

, The question asks us to work out the daily sales

Different products

The quantity and name of , Note that the data of the subject may be unique , We're going to do the data

The only change

Handle .

Everything else is easy , Just group the dates , But we have to input the name of each product , This is a little difficult . We can look at a function

group_concat

A certain field after grouping is divided into

,

Splicing is OK .

Four 、 coded

select sell_date,count(distinct product) as 'num_sold',
group_concat(distinct product order by product separator ',') as 'products'
from Activities
group by sell_date
order by sell_date 


5、 ... and 、 test result