SQL realizes 10 common functions of Excel, with original interview questions attached

SQL Is it difficult? ？ Tell the truth , Write well , It's hard. . But through SQL Written examination , It is not difficult to . I believe everyone has used Excel, use SQL Realization excel Use common operations to learn , I think it will be more specific . I have just joined the data post myself , This article is also for yourself to consolidate SQL.

SQL Interview questions 、 Technical communication , At the end of the article, ask me to get

Data is the sales data found online , Name it sale, Long like this ：

01. Correlation formula :Vlookup

vlookup yes excel Almost the most commonly used formula , It is generally used for the association query of two tables . So I first create a new table ： Copy sale Table and screen out the areas only in Guangzhou , Name it sale_guang.

create table sale_guang
SELECT * from sale where city=" Guangzhou ";

demand ： Associate the two tables according to the order detail number , also sale_guang There are only two columns: order detail number and profit

SELECT * from sale a
inner JOIN
(SELECT ordernum,profit from sale_guang) b
on a.ordernum=b.ordernum

02. Compare the differences between the two columns

demand ： contrast sale The order detail number and sale_guang Difference of order detail number ;

SELECT * from sale a
WHERE a.ordernum not in 
(SELECT b.ordernum from sale_guang b);

03. Remove duplicate values

demand ： Remove duplicate values of operator codes

SELECT * FROM sale
where salesnum not in 
(SELECT salesnum from sale
GROUP BY salesman
HAVING COUNT(salesnum)>1)

04. Missing value processing

demand ： use 0 Fill in the missing value or delete the row with the missing value of the region name .

-- use 0 fill ：
update sale set city = 0 where city = NULL
-- Delete rows with missing values ：
delete from sale where city = NULL;

05. Multi criteria screening

demand ： Want to know salesman Zhang Ai , The order amount of goods sold in Beijing is greater than or equal to 6000 Information about .

SELECT * from sale
where salesman = " Zhang Ai " 
and city = " Beijing "
and orderaccount >=6000;

06. Fuzzy filtering data

demand : The filtered inventory name contains " samsung " Or contain " SONY " Information about .

SELECT * from sale
where inventoryname like "% samsung %" 
or  Inventory name  like "% SONY %";

07. Subtotal

demand : The total profit of each salesman in Beijing .

SELECT city,sum(`profit`)
from sale
WHERE city = " Beijing "
GROUP BY `city`;

08. Conditional calculation

demand ： Inventory name includes “ Three stars ” And the tax is higher than 1000 There are several orders for ？ What is the total profit and average profit of these orders ？

-- How many ？
SELECT COUNT(*) from sale
where inventoryname like "% samsung %"
and `tax` > 1000 ;

-- What is the total profit and average profit of these orders ？
SELECT `ordernum`,SUM(profit),AVG(`profit`)
from sale
where inventoryname like "% samsung %"
and `tax` > 1000 
GROUP BY `ordernum`;

09. Delete spaces between data

demand ： Delete the space around the inventory name .

SELECT trim(inventoryname) from sale;

10. Merge and sort

demand ： Calculate the cost of each order number and sort it from high to low （ cost = Amount excluding tax - profits ）

SELECT city,ordernum,
(Nontaxamount - profit) as cost 
from sale
order by cost DESC;

summary ： Structured query language (Structured Query Language) abbreviation SQL, Sure enough, it has the same name , It's easy to query , But I want to do data processing , Can feel more than Python and excel Hard work （ Or maybe I haven't learned well orz）.

SQL The original question of the written examination

Post some I met during the interview SQL Written examination questions ：

A data service company ：

Student surface

Score surface

（1） Inquire about Student All the records in the table Sname、Ssex and Class Column .

select sname,ssex,class from student;

（2） Inquire about Score The score in the table is 60 To 80 All records between .

select * from score between 60 and 80;

（3） Inquire about 95033 Class and 95031 Class average .

select class,avg(degree) from Score a
join student b
on a.sno = b.sno
GROUP BY CLASS;

In short, it is relatively simple SQL Written examination questions , It was finished very soon . Actually, this is not the original topic , However, I have the impression that these knowledge points are investigated , And it's quite simple .

From a mobile game company SQL Pen test （ The original title is ）

（1） Create a table Student Write down the sentence , surface Student By student number Sno, full name Sname, Gender Ssex, Age Sage, Department Sdept Five attributes make up , The student number attribute cannot be empty , And its value is unique .

create table Student_new
(sno varchar(20) PRIMARY KEY,
sname varchar(10),ssex char(2),
sage int,sdept varchar(25));

（2） stay student Query in table Sdept yes “ Computer ” And press SNO Column sorting .

select * from student
where sdept = " Computer " 
order by sno ;

（3） Query in the above three tables Ccredit by 5 also Grade Greater than 60 Student's student number 、 Name and gender .

select a.sno,a.sname,a.ssex from student a
join (Course b ,SC c)
on a.sno=c.sno and b.cno =c.cno 
where Ccredit = 5 and Grade > 60;

Some Internet finance companies SQL Pen test （ The original title is ）

Full version , Come to me for

（1） surface A And table B Intersection ：

SELECT a.cus_id from ` surface a` as a
INNER JOIN ` surface b` as b
on a.cus_id=b.cus_id;

（2） surface A And table B Union ：

SELECT * from ` surface a`
UNION
SELECT * from ` surface b`;

（3） surface A And table B Symmetry difference of ：

SELECT * from ` surface a` 
where cus_id not in (SELECT * from ` surface b`)
UNION
SELECT * from ` surface b` 
where cus_id not in (SELECT * from ` surface a`);

（4） surface A Exists in but table B Does not exist in the ：

SELECT * from ` surface a`
WHERE cus_id not in (SELECT cus_id from ` surface b`);

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