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SQL exercise 4: string processing function

2022-06-10 22:27:00 【Game programming】

1 Fix the name in the table

1.1 Title Description

surface ： Users

+----------------+---------+| Column Name    | Type    |+----------------+---------+| user_id        | int     || name           | varchar |+----------------+---------+user_id  Is the primary key of the table . This table contains the user's  ID  And the name . The name consists only of lowercase and uppercase characters .

Write a SQL Query to fix the name , So that only the first character is capitalized , The rest are lowercase .
Back to press user_id Sorted result table .
An example of query result format is as follows ：

 Input ：Users table:+---------+-------+| user_id | name  |+---------+-------+| 1       | aLice || 2       | bOB   |+---------+-------+ Output ：+---------+-------+| user_id | name  |+---------+-------+| 1       | Alice || 2       | Bob   |+---------+-------+

1.2 solve

For the first time, my idea was to splice strings directly ：

select user_id,concat(upper(left(name,1)) ,lower(SUBSTRING(name,2))) as namefrom Usersorder by user_id ASC

perform ：

SQL Fourth practice ： String handling functions - The first 1 Zhang

1.3 Knowledge point

concat(str1,str2) Connect Concatenate two strings
upper(str) Capitalization String uppercase
lower(str) A lowercase letter String lowercase
LENGTH(str) length String length
SUBSTRING(str,start,end) Intercept Intercepting string ,start Start ,end end .
LEFT(str,len) Intercept Intercept the string from the left
RIGHT(str,len) Intercept Intercept the string from the right

2 Sell products by date

2.1 Title 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 、 The number of different products sold and their names .
The names of products sold on each date shall be arranged in dictionary order .
Back to press sell_date Sorted result table .
The query result format is shown in the following example ：

 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 .

2.2 solve

For repeated calculation distinct,count Count ,

select     sell_date,    count(distinct product) num_sold,     GROUP_CONCAT(distinct product) products #  By default, they are all well spliced from    activitiesgroup by sell_date # Group by date order by sell_date; #  Sort by date

perform ：

SQL Fourth practice ： String handling functions - The first 2 Zhang

2.3 Knowledge point

GROUP_CONCAT Text values inserted between values in the group . If you do not specify a separator , be GROUP_CONCAT Function uses a comma (,) As the default separator
group by By what group
order by By what sort , Default ascending order .desc Descending .

3 A patient with a disease

3.1 Title Description

Patient information sheet ： Patients

+--------------+---------+| Column Name  | Type    |+--------------+---------+| patient_id   | int     || patient_name | varchar || conditions   | varchar |+--------------+---------+patient_id （ In patients with  ID） Is the primary key of the table .'conditions' （ disease ） contain  0  One or more disease codes , Space off . This table contains information about patients in the hospital .

Write a SQL sentence , Query with I Diabetic patients ID （patient_id）、 Patient name （patient_name） And all disease codes they have （conditions）.I The code for diabetics always contains prefixes. DIAB1 .
Press In any order Return result table .
The query result format is shown in the following example .

 Input ：Patients surface ：+------------+--------------+--------------+| patient_id | patient_name | conditions   |+------------+--------------+--------------+| 1          | Daniel       | YFEV COUGH   || 2          | Alice        |              || 3          | Bob          | DIAB100 MYOP || 4          | George       | ACNE DIAB100 || 5          | Alain        | DIAB201      |+------------+--------------+--------------+ Output ：+------------+--------------+--------------+| patient_id | patient_name | conditions   |+------------+--------------+--------------+| 3          | Bob          | DIAB100 MYOP || 4          | George       | ACNE DIAB100 | +------------+--------------+--------------+ explain ：Bob  and  George  All have code to  DIAB1  Initial disease .

3.2 solve

Use locate( character , Field name ) function , If you include , return >0 Number of numbers , Otherwise return to 0 , This method can only solve the problem of containing this character , Not the prefix problem , So there will be small problems in the test .

select patient_id,patient_name,conditions from Patients wherelocate('DIAB1', conditions)>0;

Use like solve ：

select patient_id,patient_name,conditions from Patientswhere conditions like "DIAB1%"  #  front or conditions like "% DIAB1%"   #  In the middle , Notice that there are spaces

perform ：