What are the categories of sql language classification
SQL language classification which types, for this problem, this article details the corresponding analysis and solutions, hoping to help more want to solve this problem of small partners to find a simpler and easier way.
SQL languages are 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 composed of SELECT clause, FROM clause, WHERE clause.
clause:
SELECT
FROM
WHERE
2 . data manipulation language DML
There are three main forms of data manipulation language:
1)Insert: INSERT
2)Update: UPDATE
3)Delete: Delete
3. Data Definition Language DDL
Data Definition Language DDL is used to create various objects in a database---tables, views,
index, synonym, cluster, etc eg:
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 a database and to control
The database manipulates the time and effect of transactions, monitors the database, etc. 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 insert, delete, and modify operations in the database, only when transactions are committed to the data
The library is complete. Only the person who operates the database has access to the transaction before it is committed
What you do, others can only see after the final submission is completed.
There are three types of submission data: explicit submission, implicit submission, and automatic submission. Below.
Don't mention these three types.
(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, after insert, modify, delete statements are executed,
The system will automatically submit, this is automatic submission. The format is:
SQL>SET AUTOCOMMIT ON;
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