Data control language

Adata control language(DCL) is a syntax similar to a computerprogramming languageused to control access to data stored in a database (authorization). In particular, it is a component ofStructured Query Language(SQL). Data Control Language is one of the logical group in SQL Commands.SQLis the standard language for relational database management systems. SQL statements are used to perform tasks such as insert data to a database, delete or update data in a database, or retrieve data from a database.

Though database systems use SQL, they also have their own additional proprietary extensions that are usually only used on their system. For Example Microsoft SQL server uses Transact-SQL (T-SQL) which is an extension of SQL. Similarly Oracle uses PL-SQL which is their proprietary extension for them only. However, the standard SQL commands such as "Select", "Insert", "Update", "Delete", "Create", and "Drop" can be used to accomplish almost everything that one needs to do with a database.

Examples of DCL commands include:

• GRANTto allow specified users to perform specified tasks.
• REVOKEto remove the user accessibility to database object.

The operations for which privileges may be granted to or revoked from a user or role apply to both theData definition language(DDL) and theData manipulation language(DML), and may includeCONNECT,SELECT,INSERT,UPDATE,DELETE,EXECUTE,andUSAGE.

Microsoft SQL Server

As perMicrosoft SQL Serverthere are four groups of SQL Commands.

• Data Manipulation Language (DML)
• Data Definition Language (DDL)
• Data Control Language (DCL)
• Transaction Control Language (TCL)

DCL commands are used for access control and permission management for users in the database. With them we can easily allow or deny some actions for users on the tables or records (row level security).

DCL commands are:

GRANT

We can give certain permissions for the table (and other objects) for specified groups/users of a database.

DENY

bans certain permissions from groups/users.

REVOKE

this command takes away permissions from groups/users.

For example: GRANT can be used to give privileges to user to do SELECT, INSERT, UPDATE and DELETE on a specific table or multiple tables.

The REVOKE command is used take back a privilege (default) or revoking specific command like UPDATE or DELETE based on requirements.

Example

GrantSELECT,INSERT,UPDATE,DELETEonEmployeeToUser1

RevokeINSERTOnEmployeeTouser1

DenyUpdateOnEmployeetouser1

GRANT in first case we gave privileges to user User1 to do SELECT, INSERT, UPDATE and DELETE on the table called employees.

REVOKE with this command we can take back privilege to default one, in this case, we take back command INSERT on the table employees for user User1.

DENY is a specific command. We can conclude that every user has a list of privilege which is denied or granted so command DENY is there to explicitly ban you some privileges on the database objects.:

Oracle Database

Oracle Databasedivide SQL commands to different types. They are.

• Data Definition Language (DDL) Statements
• Data Manipulation Language (DML) Statements
• Transaction Control Statements
• Session Control Statements
• System Control Statement
• Embedded SQL Statements

For details referOracle-TCL

Data definition language (DDL) statements let you to perform these tasks:

• Create, alter, and drop schema objects
• Grant and revoke privileges and roles
• Analyze information on a table, index, or cluster
• Establish auditing options
• Add comments to the data dictionary

So Oracle Database DDL commands include theGrantandrevokeprivileges which is actually part of Data control Language in Microsoft SQL server.

Syntax for grant and revoke in Oracle Database:

Example

GRANTSELECT,INSERT,UPDATE,DELETEONdb1.EmployeeTOuser1;

REVOKESELECT,INSERT,UPDATE,DELETEONdb1.EmployeeFROMuser1;

Transaction Control Statements in Oracle

Transaction control statements manage changes made by DML statements. The transaction control statements are:

• COMMIT
• ROLLBACK
• SAVEPOINT
• SET TRANSACTION
• SET CONSTRAINT

MySQL

MySQLserver they divide SQL statements into different type of statement

• Data Definition Statements
• Data Manipulation Statements
• Transactional and Locking Statements
• Replication Statements
• Prepared Statements
• Compound Statement Syntax
• Database Administration Statements
• Utility Statements

For details referMySQL Transactional statements

The grant, revoke syntax are as part of Database administration statementsàAccount Management System.

The GRANT statement enables system administrators to grant privileges and roles, which can be granted to user accounts and roles. These syntax restrictions apply:

• GRANT cannot mix granting both privileges and roles in the same statement. A given GRANT statement must grant either privileges or roles.
• The ON clause distinguishes whether the statement grants privileges or roles:
• With ON, the statement grants privileges
• Without ON, the statement grants roles.
• It is permitted to assign both privileges and roles to an account, but you must use separate GRANT statements, each with syntax appropriate to what is to be granted.

The REVOKE statement enables system administrators to revoke privileges and roles, which can be revoked from user accounts and roles.

Examples

REVOKEINSERTON*.*FROM'jeffrey'@'localhost';

REVOKE'role1','role2'FROM'user1'@'localhost','user2'@'localhost';

REVOKESELECTONworld.*FROM'role3';

GRANTALLONdb1.*TO'jeffrey'@'localhost';

GRANT'role1','role2'TO'user1'@'localhost','user2'@'localhost';

GRANTSELECTONworld.*TO'role3';

InPostgreSQL,executing DCL istransactional,and can be rolled back.

GrantandRevokeare the SQL commands are used to control the privileges given to the users in a Databases

SQLitedoes not have any DCL commands as it does not have usernames or logins. Instead, SQLite depends onfile-system permissionsto define who can open and access a database.

See also

• Data definition language
• Data manipulation language
• Data query language