DQL, DML, DDL, DCL

Most database companies work to address this problem in two ways:
(1) Expand SQL, introduce the procedural structure in SQL, (2) Embed SQL into the high-level language,
In order to complete a complete application together.

Two. Classification of SQL languages

The 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 DQL basic structure of the data query language is determined by the SELECT clause, the FROM clause, where
clause consists of a query block:
SELECT < field Name table >
From < table or view name >
WHERE < query conditions >

2. Data manipulation language DML
There are three main forms of data manipulation language DML:
1) Inserting: Insert
2) Updates: Update
3) Remove: Delete

When the Execute DML command is not committed, it will not be seen by other sessions. Unless a DDL command or DCL command is executed after the DML command, or the user exits the session or terminates the instance, the system automatically issues a commit command that commits the uncommitted DML command

3. Data Definition Language DDL
The data definition language DDL is used to create various objects in the database-----tables, views,
indexes, synonyms, clusters, etc.:
CREATE Table/view/index/syn/cluster
| | | | |
Table View index synonym cluster

DDL operations are implicitly committed! Can't rollback

DDL (data definition Language)

CREATE table creating tables    ALTER TABLE  modify tables   drop table Delete tables   TRUNCATE TABLE delete all rows in tables    CREATE index   drop Index  Delete Index when executing a DDL statement, Oracle commits the current transaction before and after each statement. If the user inserts a record into the database using the Insert command, a DDL statement (such as CREATE table) executes, and the data from the Insert command is committed to the database. When the DDL statement execution completes, the DDL statement is automatically committed and cannot be rolled back.

4. Data Control Language DCL
Data Control Language DCL is used to grant or reclaim some kind of privilege to access a database and to control
The time and effect of database manipulation transaction, and the monitoring of database. Such as:
1) Grant: authorization.

2) ROLLBACK [work] to [savepoint]: fallback to a point.
Roll Back---ROLLBACK
The rollback command brings the database state back to the last committed state. The format is:
sql>rollback;

3) Commit [work]: Submit.

When a database is inserted, deleted, and modified, only when the transaction is committed to the data
Only when the library is complete. Before a transaction is committed, only the person who operates the database will be able to see
To do things, others can only be seen after the final submission is completed.
There are three types of submission data: explicit commit, implicit commit, and auto-commit. The following points
Do not describe these three types.

(1) Explicit submission
Commits that are completed directly with the commit command are explicitly committed. The format is:
sql>commit;

(2) Implicit submission
Commits that are indirectly completed with SQL commands are implicitly committed. These commands are:
Alter,audit,comment,connect,create,disconnect,drop,
Exit,grant,noaudit,quit,revoke,rename.

(3) Automatic submission
If the autocommit is set to ON, after the insert, modify, DELETE statement executes,
The system will commit automatically, which is automatic submission. The format is:
Sql>set autocommit on;

DQL, DML, DDL, DCL