Niuke brush questions - MySQL series

  Preface

Author's brief introduction ： Hello, friends , I'm your classmate Xiao Wang

Personal home page ： Xiao Wang

Series column ： Niu Ke brushes the question column

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Today's question brushing series is ：

Mysql series    mysql Direct link of question brushing  mysql Brush problem

 

 

  There are many question banks Knowledge of heel Sutra I really have a good conscience ！！

  Title Description

Query all columns _ Niuke Tiba _ Cattle from (nowcoder.com)

Their thinking

This way sql There are two solutions to the problem

1.SELECT * from user_profile;

2.SELECT id,device_id,gender,age,university,province from user_profile;

If you compare the performance recommend The second kind

Code details

SELECT * from user_profile;

SELECT id,device_id,gender,age,university,province from user_profile;

 

too spicy ！！~~ 

Title Description

Query multiple columns _ Niuke Tiba _ Cattle from (nowcoder.com)

Their thinking

This question is based on the requirements of the question Put the query column Just list the queries one by one

Code details

select 
device_id,gender,age,university
from user_profile;

Too spicy ~~ 

Title Description

Query result de duplication _ Niuke Tiba _ Cattle from (nowcoder.com)

Their thinking

use DISTINCT Keyword can remove duplicate lines in the result .
DISTINCT Keywords in SELECT Behind the word 、 The front of the target column name sequence .

Code details

select distinct university from user_profile;

Too spicy ~~ 

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