[MySQL learning] 8

insert into cellphone values(null,‘vivo mobile phone ’,3600,0.88);

insert into cellphone values(null,‘ Huawei mobile phones ’,5500,0.92);

insert into cellphone values(null,‘ Meizu mobile phone ’,3400,0.95);

insert into cellphone values(null,‘ Pineapple mobile phone ’,8000,0.90);

After successfully creating the table, enter select * from cellphone; Check whether the data is inserted successfully , If shown as follows , Then our preparations are finished .

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Use the alias

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When we query data , The query column names are often not very semantic , for example , The list of mobile phones shown above is name, It's the name , What's the name ？ It's not clear .

as The usage of is Old column names as New column names

Now? , We use as To define aliases , hold name Change to mobile phone name .

select name as ‘ Mobile name ’, price, discount from cellphone;

We use as Post semantic is much stronger .

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Perform calculations on multiple columns

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When we look at this table, we will find , Mobile phones have a price , 《 A big factory Java Analysis of interview questions + Back end development learning notes + The latest architecture explanation video + Practical project source code handout 》 Free open source Prestige search official account 【 Advanced programming 】 There is also a discount , Then the actual price of the mobile phone is the current price * discount , We want to check the actual price now. What should we do ？ There is no actual price field in the table , At this time, we can perform arithmetic operations on multiple columns .

The format of operations performed by multiple columns is     Name 1 Operator Name 2… as New column names , To enhance semantics , You can use a bracket to wrap the columns of operations .

Now? , Let's check the actual price of the mobile phone through calculation

select * ,(price * discount) as ‘ The actual price ’ from cellphone;

We use columns to calculate the current actual price , But we find that the actual price has a lot of decimals , Can we just keep 2 Decimal places ？ It certainly can , Later, we can use functions to realize , I won't introduce .

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