Database Learning Notes

Definition of L:

SQL is the standard computer language for accessing and working with databases.

• SQL refers to the Structured Query language, the full name is Structured query Language.
• SQL allows you to access and manipulate the database.
• SQL is a computer language of ANSI (American National Standards Institute United States Standardization Organization) standard.

2.RDBMS

• RDBMS refers to the relational database management system, the full name of relational databases Management system.
• The RDBMS is the foundation of SQL and is also the foundation of all modern database systems, such as MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
• Data in an RDBMS is stored in a database object called a table.
• A table is a collection of related data items that consists of columns and rows.

3.SQL syntax

• Use database name; command to select a database.
• set names UTF8; The command is used to set the character set used.
• SELECT * from Websites; Read the data table information.
• SQL is not case sensitive: Select is the same as select.
• SELECT statement

SELECT name,country from Websites;

SELECT DISTINCT country from Websites; // the SELECT DISTINCT statement is used to return only different values. 

SELECT * from Websites WHERE country='CN';

• and & OR Operators

SELECT * from websiteswhere country='CN';

SELECT * from websiteswhere country='USA'OR Country=' CN ';

• ORDER BY syntax

SELECT * from websitesorder by Alexa; // the default is in ascending order, that is, select * from Websites order by Alexa ASC

SELECT * from websitesorder by Alexa DESC;

• INSERT INTO syntax

The first form does not need to specify the column name to insert the data, just provide the inserted value:

INSERT into Table_namevalues (Value1,value2,value3,...);

The second form requires specifying the column name and the value to be inserted:

INSERT into table_name (COLUMN1,COLUMN2,COLUMN3,...) VALUES (Value1,value2,value3,...);

• Update syntax

UPDATE Websites SET alexa='country= ', 'USA'  WHERE name=' Rookie tutorial ';

Take extra care when updating records! In the above example, if we omit the WHERE clause, all Alexa and country in the data will be changed

• Delete syntax

DELETE from websiteswhere name=' Baidu ' and country='CN  ';

• Select top, limit, rownum syntax

Not all database systems support the SELECT top syntax, the following is the Sql,ms Access database system

 PERCENT * from Websites;

MY SQL Database System

SELECT column_name (s) from table_namelimit number;

Oracle Database System

SELECT *<=5;

Like operator

SELECT *'g%' *'%oo%';

wildcard characters	Description
%	Override one or more characters
_	Replaces only one character
[Charlist]	Any single character of the word columns
[^charlist] Or [!charlist]	Not any single columns of the word

Database Learning Notes