The full name of sql is Structured Query Language, which is a special-purpose programming language. It is a database query and programming language used to access data, query, update and manage relationships. The database system is also the extension of the database script file.
SQL is a high-level non-procedural programming language that allows users to work on high-level data structures. It does not require users to specify the data storage method, nor does it require users to understand the specific data storage method, so different database systems with completely different underlying structures can use the same structured query language as the interface for data input and management. Structured Query Language statements can be nested, which makes it extremely flexible and powerful.
Structured Query Language SQL contains 6 parts:
1. Data Query Language (DQL: Data Query Language):
its statements, Also called a "data retrieval statement", it is used to obtain data from a table and determine how the data is presented in the application. The reserved word SELECT is the most commonly used verb in DQL (and all SQL). Other commonly used reserved words in DQL include WHERE, ORDER BY, GROUP BY and HAVING. These DQL reserved words are often used with other types of SQL statements.
2. Data Manipulation Language (DML):
Its statements include the verbs INSERT, UPDATE and DELETE. They are used to add, modify and delete rows in the table respectively. Also known as Action Query Language.
3. Transaction Processing Language (TPL):
Its statements can ensure that all rows of the table affected by the DML statement are updated in a timely manner. TPL statements include BEGIN TRANSACTION, COMMIT and ROLLBACK.
4. Data Control Language (DCL):
Its statements obtain permission through GRANT or REVOKE to determine the access of individual users and user groups to database objects. Some RDBMS can use GRANT or REVOKE to control access to individual columns of a table.
5. Data Definition Language (DDL):
Its statements include the verbs CREATE and DROP. Create a new table or delete a table (CREAT TABLE or DROP TABLE) in the database; add indexes to the table, etc. DDL includes many reserved words related to obtaining data in human database directories. It is also part of the action query.
6. Pointer Control Language (CCL):
Its statements, such as DECLARE CURSOR, FETCH INTO and UPDATE WHERE CURRENT, are used to operate on individual rows of one or more tables.
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