Database section---Add/remove databases, add/delete tables, add data to the database;

One:

1. Create a database

Create Database test2;

2. Delete the database;

Drop database test2;

3. Create a table;

CREATE TABLE Test

(

Code varchar (20),

Name varchar #varchar是字符串类型, need to add length (), code and name are the names of the created columns, a column to write a comma, the last column without commas.

); #是数据库的注释语法.

Garther:

CREATE TABLE Test1

(

Code varchar PRIMARY KEY, #primary key for the primary key, so the code column becomes the primary key.

Name varchar (20)

);

Set name to non-null:

CREATE TABLE Test2

(

Code varchar (primary key),

Name varchar is NOT NULL #not NULL is NOT NULL, so the name column is required by the user.

);

FOREIGN key relationships

Create TABLE Zhu

(

Code int PRIMARY KEY,

Name varchar (20)

);

CREATE TABLE Cong

(

Code int PRIMARY KEY,

Name varchar (20),

Zhu Int, # Adds a foreign key relationship to this column, which is the same type as the primary key type in the Zhu table

Foreign key (Zhu) references Zhu (code) #foreign key foreign Key (Zhu) references Zhu (code) (Zhu) refers to the Zhu table Code column

);

Self-growing column: (When the primary key is not found), add a new column, let it be the primary key, this column is the self-growing column, this column of data from the growth, do not need to add data, but it is meaningless.

CREATE TABLE Haoyou

(

IDS int Auto_increment primary KEY, # auto_increment keyword, so this column is self-growing

Name varchar (20),

Friends varchar (20)

);

4. Delete the table:

drop table haoyou;

Note: A. Add a semicolon after each statement

B. Last column cannot be comma-added

C. Write the full format in English.

5. Modify the statement for the table:

Two. Adding and removing data: crud operation, c for Create Add, R for read query, u for update modification, D for delete delete

1.C: Add Data

CREATE TABLE Test5

(

Code varchar (primary key),

Name varchar (NOT NULL)

);

INSERT into test2 values (' n001 ', ' Zhang San ');

Attention:

A insert into table name values (the data added in parentheses, if it is a string, use single quotation marks, if other types, do not add single quotation marks.) )

b INSERT into test2 values (' n001 ', '); When you add only one value, the other adds ', ' and nothing is written inside.

C INSERT into test2 (' n001 '); only add data to the Code column in Test2, you need to append the name of the column to the table name.

D If the table you want to add has a self-growing column, you can add an empty string to the self-growing column, insert into haoyou values (', ' LZ ', ' sz ');

Examples:

Table creation

Create Table  intprimarykeyvarchar (double  double double) ; 

Add Data:

Database section---Add/remove databases, add/delete tables, add data to the database;