Database foundation

Catalog

Database operation

Table operations

data type

value type

String type

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DDL Basic statement of database operation  

Database operation

  Those in square brackets are optional .

if not exist If it doesn't exist , Then establish a database .

Input show databases; Regret shows a little 4 A database , These are all mysql The database that comes with it .

Suppose you have created a database , Want to create another database with the same name , So it's a mistake .

  If you don't want this to happen , Then you can use the following code ：

create database if not exists itcast;

 

  Input statement before quick query ： Directly press the up and down keys to view

If you forget your current database , Direct input select database();

data type

value type

 score double（4,1） What is shown here is that the fraction is at most four digit precision （100.0 There are four bits ）, The maximum scale is 1 position （ That is, at most one decimal ）

String type

char Performance ratio of varchar It is better to .

 

Table operations

First of all use Specific databases , To be able to show Out of the right tables;

 

 

  Follow the above naming method , We can set up the corresponding table

Table operations —— add rows  

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Table operations —— modify