Introduction and advanced MySQL (4)

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1、 What is? SQL

The name of our course is MySQL, But it's not learning MySQL, It's learning SQL.SQL Call it structured query language , Is a set of language used to operate the database . We installed the database yesterday , You need to access the data inside , What you use is SQL Language .
And all relational databases support SQL, in other words We learned SQL You can operate at the same time Oracle MySQL SqlServer. Because most databases SQL Basically the same （ Note that there are also some differences ）

Structured query language (Structured Query Language) abbreviation SQL( pronunciation ：/ˈes kjuː ˈel/ “S-Q-L”), Is a special purpose programming language , Is a database query and programming language , For data access and query 、 Update and manage relational database system ; It is also the extension of database script file .

2、SQL classification

One ： Data query language （DQL:Data Query Language）：

Its statement , Also known as “ Data retrieval statements ”, To get data from a table , Determine how the data is presented in the application . Reserved words SELECT yes DQL（ Also all SQL） The most used verb , other DQL The common reserved words are WHERE,ORDER BY,GROUP BY and HAVING. these DQL Reserved words are often associated with other types of SQL Statement together .

Two ： Data operation language （DML：Data Manipulation Language）：

Its sentences include verbs INSERT,UPDATE and DELETE. They are used to add , Modify and delete rows in the table . Also known as action query language .
database ： Additions and deletions check select DQL operation Additions and deletions insert update delete DML operation

3、 ... and ： Transaction language （TPL）：

Its statement ensures that it is DML All rows of the table affected by the statement are updated in time .TPL Statements include BEGIN TRANSACTION,COMMIT and ROLLBACK.

Four ： Data control language （DCL）：

Its sentences are passed through GRANT or REVOKE Get permission to , Determine the access of individual users and user groups to database objects . some RDBMS You can use GRANT or REVOKE Control access to form columns .

5、 ... and ： Data definition language （DDL）：

Its sentences include verbs CREATE and DROP. Create a new table or delete a table in the database （CREAT TABLE or DROP TABLE）; Index the table, etc .DDL It includes many reserved words related to obtaining data in the human database directory . It's also part of the action query .

6、 ... and ： Pointer control language （CCL）：

Its statement , image DECLARE CURSOR,FETCH INTO and UPDATE WHERE CURRENT For actions that are unique to one or more forms .