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This article mainly introduces what is the type of database operation, with a certain reference value, friends need to refer to the next. I hope you all have a lot to gain after reading this article. Let's take a look at it together.

SQL language is divided into four categories: data query language DQL, data manipulation language DML, data definition language DDL, data control language DCL.

1. Data Query Language DQL

The basic structure of DQL is a query block consisting of SELECT clause, FROM clause and WHERE clause:

SELECT

FROM

WHERE

Data Manipulation Language (DML)

There are three main forms of data manipulation language:

1)Insert: INSERT

2)Update: UPDATE

3)Delete: Delete

Data Definition Language DDL

DDL is used to create various objects in a database-tables, views, indexes, synonyms, clusters, etc. such as:

CREATE TABLE/VIEW/INDEX/SYN/CLUSTER | | | | | table View index synonym cluster

DDL operations are implicitly committed! No rollback.

4. Data Control Language DCL

Data Control Language (DCL) is used to grant or withdraw certain privileges to access databases, control the time and effect of database manipulation transactions, and monitor databases. For example:

1)GRANT: Authorization.

2)ROLLBACK [WORK] TO [SAVEPOINT]: Back to a certain point.

Rollback---ROLLBACK

The rollback command returns the database state to the last commit state. The format is SQL>ROLLBACK.

3)COMMIT [WORK]: Submit.

During database insert, delete, and modify operations, the transaction is complete only when committed to the database. Before a transaction commits, only the person who operates the database has the right to see what has been done, and others can only see it after the final commit is complete.

There are three types of submission data: explicit submission, implicit submission, and automatic submission.

These three types are described below.

(1)explicitly commit

Commits that are done directly with the COMMIT command are explicit commits. The format is SQL>COMMIT;

(2)implicit commit

Commitments done indirectly with SQL commands are implicit commits. These orders are:

ALTER，AUDIT，COMMENT，CONNECT，CREATE，DISCONNECT，DROP，EXIT，GRANT，NOAUDIT，QUIT，REVOKE，RENAME。

(3)autocommit

If AUTOCOMMIT is set to ON, the system will automatically commit after the insertion, modification and deletion statements are executed. This is automatic commit.

SQL>SET AUTOCOMMIT ON

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