In short database is stored data warehouse, is a collection of data in order to achieve a certain purpose, according to certain rules organized.
So we have a common database model:
1, a relational database
MySql
Oracle
SQL Server
2, non-relational database
2,1 document storage database MongDB
2,2 key-value store database Redis Memcached
2, 3, column-store database HBase
2,4 graphical database Neo4J
About database in the company subject of the interview are those who do?
1, SQL database operation statement
2, SQL statement action table structure
3, the relationship between the attributes and the relationships between fields and tables class
Table corresponding to the java classes, the database used to store data fetched
Field name (column) and class member variables of the same properties
Objects rows in a table created from class
3, SQL statement presentation:
MySql do not know java, then you need to interact with the database required to know the language
SQL statement is a data code library
4, SQL classification
4,1 Data Definition Language DDL for a database table definitions and column Keywords: create alter drop
4,2 database operations DML statement is used to update the keyword database tables: insert delete updata
4,3 DCL statement Database control for database access permissions and security levels
4,4 DQL query the database for records subject keyword: select from where
5, SQL general syntax:
1, case-insensitive
2, keyword suggestions uppercase
6, comments:
- Single-line comments // single line comment # single line comment multi-line comments / ** /
7, data types
int (integer) Integer
decimal (m, d) decimal precision
date includes the date, time does not include the minutes and seconds
datetime include date, it included minutes and seconds
timetamp contains period, a time stamp
varchar (m) 0-65535 m represents a string length
8, we generally create a database of grammar and Methods: Focus
8,1 create a database
create database database name;
8,2 View database
show databases; this is to look at all of the database
The new show create database database name;
8,3 delete database
drop database database name;
8,4 query the database name is being used
select database（）；
8,5 convert the database
use database name;
The following look at an example:
# Create a database
the CREATE DATABASE day02;
# database change
the USE day02;
# database query
the SELECT DATABASE ();
# delete the database
DROP DATABASE day02;
# View database
SHOW DATABASES;
# see the new database
SHOW CREATE DATABASE day02;
9, create a database table
9,1 create a database table:
Syntax: create table table name (
Column Name Data Type,
Column Name Data Type
）；
9.2 database table constraints
[] May be omitted on a column of data to be limiting a primary key constraint limits can not be empty of data can not be repeated
The only constraints a null data can not not be repeated
A non-null data constraints can not be empty
9,3 Table View
show tables;
9,4 see table structure
DESC table name;
9.5 modify the table name
raname table the old table to the new table name;
9,6 modify table structure
alter table name;
Syntax: alter table table add Column Name Data Type ();
9,7 Modify columns constraint length
modify（）；
# Create a data table SHOW TABLE; # View table structure DESC ruirui; # modify the table name RENAME TABLE ruirui the TO haohao; SHOW TABLE; DESC haohao; # create a data table the CREATE TABLE ruirui ( carid INT, in the Password VARCHAR ( 15 ), `name` VARCHAR ( 10 ), Sex VARCHAR ( 2 ), Age the INT ); # Display SHOW tABLES; DESC ruirui; # table modify the RENAME the TO tABLE ruirui huahua; DESC huahua;