Data Control Language (DCL) Statements
Data Control Language Statements are used to grant privileges on tables, views, sequences, synonyms, procedures to other users or roles.
The DCL statements are
GRANT :Use to grant privileges to other users or roles.
REVOKE :Use to take back privileges granted to other users and roles.
Privileges are of two types :
System Privileges
Object privileges
System Privileges are normally granted by a DBA to users. Examples of system privileges are CREATE SESSION, CREATE TABLE, CREATE USER etc.
Object privileges means privileges on objects such as tables, views, synonyms, procedure. These are granted by owner of the object.
Object Privileges are
ALTER
Change the table definition with the ALTER TABLE statement.
DELETE
Remove rows from the table with the DELETE statement.
Note: You must grant the SELECT privilege on the table along with the DELETE privilege.
INDEX
Create an index on the table with the CREATE INDEX statement.
INSERT
Add new rows to the table with the INSERT statement.
REFERENCES
Create a constraint that refers to the table. You cannot grant this privilege to a role.
SELECT
Query the table with the SELECT statement.
UPDATE
Change data in the table with the UPDATE statement.
Note: You must grant the SELECT privilege on the table along with the UPDATE privilege.
Grant
Grant is use to grant privileges on tables, view, procedure to other users or roles
Examples
Suppose you own emp table. Now you want to grant select,update,insert privilege on this table to other user “SAMI”.
grant select, update, insert on emp to sami;
Suppose you want to grant all privileges on emp table to sami. Then
grant all on emp to sami;
Suppose you want to grant select privilege on emp to all other users of the database. Then
grant select on emp to public;
Suppose you want to grant update and insert privilege on only certain columns not on all the columns then include the column names in grant statement. For example you want to grant update privilege on ename column only and insert privilege on empno and ename columns only. Then give the following statement
grant update (ename),insert (empno, ename) on emp to sami;
To grant select statement on emp table to sami and to make sami be able further pass on this privilege you have to give WITH GRANT OPTION clause in GRANT statement like this.
grant select on emp to sami with grant option;
REVOKE
Use to revoke privileges already granted to other users.
For example to revoke select, update, insert privilege you have granted to Sami then give the following statement.
revoke select, update, insert on emp from sami;
To revoke select statement on emp granted to public give the following command.
revoke select on emp from public;
To revoke update privilege on ename column and insert privilege on empno and ename columns give the following revoke statement.
revoke update, insert on emp from sami;
Note :You cannot take back column level privileges. Suppose you just want to take back insert privilege on ename column then you have to first take back the whole insert privilege and then grant privilege on empno column.
ROLES
A role is a group of Privileges. A role is very handy in managing privileges, Particularly in such situation when number of users should have the same set of privileges.
For example you have four users :Sami, Scott, Ashi, Tanya in the database. To these users you want to grant select ,update privilege on emp table, select,delete privilege on dept table. To do this first create a role by giving the following statement
create role clerks
Then grant privileges to this role.
grant select,update on emp to clerks;
grant select,delete on dept to clerks;
Now grant this clerks role to users like this
grant clerks to sami, scott, ashi, tanya ;
Now Sami, Scott, Ashi and Tanya have all the privileges granted on clerks role.
Suppose after one month you want grant delete on privilege on emp table all these users then just grant this privilege to clerks role and automatically all the users will have the privilege.
grant delete on emp to clerks;
If you want to take back update privilege on emp table from these users just take it back from clerks role.
revoke update on emp from clerks;
To Drop a role
Drop role clerks;
LISTING INFORMATION ABOUT PRIVILEGES
To see which table privileges are granted by you to other users.
SELECT * FROM USER_TAB_PRIVS_MADE
To see which table privileges are granted to you by other users
SELECT * FROM USER_TAB_PRIVS_RECD;
To see which column level privileges are granted by you to other users.
SELECT * FROM USER_COL_PRIVS_MADE
To see which column level privileges are granted to you by other users
SELECT * FROM USER_COL_PRIVS_RECD;
To see which privileges are granted to roles
SELECT * FROM USER_ROLE_PRIVS;
