MySQL learning record (2)

1. Create database

For the time being MYSQL

create database shop;
/* Create database */
show databases;
/* Show the current MYSQL Stored database */

2. Create table

CREATE TABLE <  Table name  >
( <  Name  1> <  data type  > <  Constraints required for this column  > ,
  <  Name  2> <  data type  > <  Constraints required for this column  > ,
  .
  .
  .
  <  Constraints for this table  1> , <  Constraints for this table  2> ,……);
create database shop;
use shop;
CREATE TABLE product(
     product_id CHAR(4) NOT NULL, 
     product_name VARCHAR(100) NOT NULL, 
     product_type VARCHAR(32) NOT NULL, 
     sale_price INTEGER, 
     purchase_price INTEGER, 
     regist_date DATE, 
     PRIMARY KEY(product_id)
 )  ;

  The syntax is shown in the code , But if you want to create a table under the currently created database , To use use < Database name >, no need USE The complains .

 

Perform shortcut key sharing ：ctrl+enter  Execute the currently selected command line , If it is not selected, the current line will be executed

                            ctrl+shift+enter  Execute all commands

                            ctrl+shift+r  Run only the selected statements

3. Naming rules

• Only half width English letters can be used 、 Numbers 、 Underline （_） As a database 、 Table and column names
• The name must start with half letter
• Every field in every table （ That is, each column ） Specify the data type

3.1 Basic types of data

• INTEGER type （INT, Similar to floating point , Double precision ）

Used to specify the data type of the column where integers are stored （ Digital ）, Can't store decimals .

• CHAR type （ character string =string）

Used to store fixed length strings , When the length of the string stored in the column does not reach the maximum length , Use half space to complement , Because it wastes storage space , So I don't use .

• VARCHAR type （ Variable length string ）

Used to store variable length strings , Fixed length string will be supplemented with half width spaces when the number of characters does not reach the maximum length , But variable length strings are different , Even if the number of characters does not reach the maximum length , I don't use half space to make up .

• DATE type （ date ）

Used to specify the storage date （ Specific date ） The data type of the column of （ Date type ）.

3.2 Setting of data constraints

Constraints are in addition to data types , The function of restricting or appending conditions to the data stored in a column .

NOT NULL yes Non empty constraint , That is, data must be entered in the column .

PRIMARY KEY yes Primary key constraint , Represents that the column is unique , You can get the data of a specific row through this column .

There is no need to restrict

3.3 About table deletion and update syntax

similar stata

• Delete table ：drop table < Table name >; （stata :drop  Field name ）
• Modify table —— The main use of ALTER command

              Add columns to the table ：alter table < Table name > add column< Definition of columns >;

              Delete column from table ：alter table< Table name >drop column< Name >;

• Clear the table ：truncate table table_name

alter table product  add column quality INTEGER;
-- Add a column... To the table , Field called quality
alter table product drop column quality ;
-- Delete a column from the table , Field called quality
drop table product;

feeling ： At present, the grammar is ok , If someone used a similar language before , It should be easier to learn this .

  I watched the tutorial from Alibaba cloud Tianchi  , For personal notes only .