Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:
- CREATE - to create objects in the database
- ALTER - alters the structure of the database
- DROP - delete objects from the database
- TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
- COMMENT - add comments to the data dictionary
- RENAME - rename an object
Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
- SELECT - retrieve data from the a database
- INSERT - insert data into a table
- UPDATE - updates existing
data within a table
- DELETE - deletes all records from a table, the space for the records remain
- MERGE - UPSERT operation (insert or update)
- CALL - call a PL/SQL or Java subprogram
- EXPLAIN PLAN - explain access path to data
- LOCK TABLE - control concurrency
DML commands can't be
For revoking the transactions and to make the data commit to the database we use TCL. Some of the TCL commands are:
ROLLBACK is used for revoking the transactions until last commit.
COMMIT is used for commiting the transactions to the database.
Once we commit we cannot rollback. Once we rollback we cannot commit.