MySQL database review _day01_ & SQL database describes basic operations

Database Introduction

Basic concepts of database

① concept

• English word database: DataBase;
• The database is used to store and manage data warehouses.

② Features

• Persistent storage of data. In fact, the database is a file system
• Easy to store and manage data
• Use a unified approach to operational database - SQL

2. Common database software

• MySQL: free open source database, small database, Oracle has been acquired. MySQL6.x version also start charging. Later, Sun's acquisition of MySQL, Oracle and Sun Microsystems has been acquired
• Oracle: charges of large-scale databases, Oracle's products.
• DB2: IBM's database products and fees. Often used in the banking system.
• SQL Server: database MicroSoft medium-sized companies for a fee. C # ,. net and other languages ​​commonly used.
• SQLite: Embedded small database applications in mobile terminal, such as: Android.

SQL basic operations

1. What is SQL?

• Structured Query Language: Structured Query Language;
• In fact, it defines all the rules of relational database operations.

2. SQL syntax common

• SQL statements can be single or multiple rows of writing, end with a semicolon.
• You can use spaces to indent and enhance the readability of the statement.
• MySQL database SQL statements are not case sensitive, use uppercase keyword suggestions.
• Three kinds of comments
  • Single-line comments: - Annotation content annotation content or # (mysql-specific)
  • Multi-line comments: / * comment * /

3. SQL classification

① DDL (Data Definition Language) data definition language

• It is used to define the database objects: databases, tables, columns and the like. Keywords: create, drop, alter, etc.

② DML (Data Manipulation Language) data manipulation language

• The data tables in the database used to additions and deletions. Keywords: insert, delete, update, etc.

③ DQL (Data Query Language) data query language

• Used to query records (data) tables in the database. Keywords: select, where, etc.

④ DCL (Data Control Language) database control language (understanding)

• To define the access permissions and security levels, and create user database. Keywords: GRANT, REVOKE, etc.

DDL: operation of the database, table

CRUD 1. Operation of the database

① C (Create): Creating

• Create a database
  create database database name;
• Create a database, judgment does not exist, then create:
  the Create Database not IF EXISTS database name;
• Create a database and specify the character set
  create database database name of the character set the character set name
• The sample code

create database if not exists db1 character set GBK;

② R (Retrieve): inquiry

• All queries the database name:
  Show Databases;
• Query a database character sets: a database query creation statements
  show create database database name;

③ U (Update): modify

• Modify the database character set of
  alter database database name of the character set the character set names;

④ D (Delete): Delete

• Delete database
  drop database database name;
• Judgment database exists, then there is deleted
  drop database if exists database name;

⑤ use the database

• Query the database name currently in use
  select database ();
• Using the database
  use the database name;

CRUD 2. Operating data table

① C (Create): Creating

• grammar:

create table 表名(
	列名1 数据类型1,
	列名2 数据类型2,
	....
	列名n 数据类型n
);

• Database type:

  • int: integer type

  • double: decimal type

  • date: date, containing only the date, yyyy-MM-dd

  • datetime: date, time of year, month, day, hour comprising yyyy-MM-dd HH: mm: ss

  • timestamp: the time stamp type comprising Minutes yyyy-MM-dd HH when date: mm: SS
    * If this field does not give future assignment, or the assignment is null, the current system time is used by default, automatically assigned

  • varchar: String
    * name varchar (20): name up to 20 characters
    * zhangsan 8 characters seating two characters

• The sample code

create table student(
	id int,
	name varchar(32),
	age int ,
	score double(4,1),
	birthday date,
	insert_time timestamp
);

• Copy the table:
  the table name create table table name like to be copied;

② R (Retrieve): inquiry

• The name of a query for all tables in the database
  show tables;
• Lookup table structure
  desc table name;

③ U (Update): modify

• Modify the table name
  alter table table name rename to new table name;
• Modify the character set table
  alter table table name character set the character set name;
• Add an
  alter table table add Column Name Data Type;
• Column Name Type modifications
  alter table change table column names new column not new data types;
  alter table column name table modify the new data type;
• Remove Columns
  alter table table name drop column names;

④ D (Delete): Delete

• drop table name;
• drop table if exists 表名 ;

DML: deletions in the data table changes

1. Add data

• grammar

insert into 表名(列名1,列名2,...列名n) values(值1,值2,...值n);

• note
  • Column names and values ​​to one correspondence.
  • If the table name, column name is not defined, the default value is added to all columns
    insert into table values (value 1, value 2, ... n-value);
  • In addition to digital type, other types require the use of quotation marks (single or double can be) cause to

2. Delete Data

• grammar:

delete from 表名 [where 条件]

• note:
  • If not conditions, all records in the table is deleted.
  • If you want to delete all records
    1. delete from table name; - not recommended. How many records will be executed many times the deletion
    2. TRUNCATE TABLE table name; - recommended to use, more efficient to delete the table, and then create a different table.

3. Modify the data

• grammar:

update 表名 set 列名1 = 值1, 列名2 = 值2,... [where 条件];

• note:
  • If you do not add any conditions, then all records in the table all the changes.