When I forget how to write SQL, I

When I forget SQL How to write , I ……

What I used to be , Open the computer Baidu , Open the notes for a round of inquiry , I didn't find what I wanted most . Learn how to learn MySQL

Don't panic , No big problem

It turned out MySQL It comes with help documents .

So I had a meal to operate ：win+R >> mysql -uroot -p >>  Enter ：？

result ： The face is as green as the words in the picture , I can't understand what chicken intestines are written

I can't understand. It's OK , Teach now

Explain through chestnuts

For example, modify the table field name , I remember this order , yes , yes alter    forehead , I just remember it was alter 了

No big problem , Do you remember alter

First step ： Ask next alter,alter How to use it?

? alter

The second step ： Ask again alter table

? alter table

So this version （5.7.27） I won't support it …… So you use rename There is no way to modify the field name .

When I change mysql 8.0.27 after , See support rename Grammar is like this , More than a bar ……

The third step ： Merge grammar

Summon the snake skin monster

alter table tbl_name rename column old_col_name to new_col_name;

Test it , See if the fit succeeds

Hey 、 As if , I got hold of MySQL help file

In case 、 I forgot how to spell alter 了 , What do I do ？

Ask no questions ？？？ Slightly , Look at the picture and see how to ask

Data Definition   (DDL  Data definition statement )
Data Manipulation (DML  Data operation statement )
Data Types ( data type )

See here is not an instant understand it ,DDL and DML  All found ​.

pursuant to an inquiry , You see , This is back to the first step before

Only this and nothing more , You have mastered how to catch fish at work ​. Teaching a man to fish is better than giving him a fish ​！！

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