DDL, DML & DCL Commands in SQL

Mohammed Imtiyaz Nov 26, 2014

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DDL statements are used to define the database structure or schema. Some examples are as follows:

CREATE	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

DML statements are used for managing data within schema objects. Some exmples are as follows:

SELECT	Retrieve data from the database
INSERT	Inser data into a table
UPDATE	Updates existing data within a table
DELETE	Deletes all records from a table.
MERGE	UPSERT operation (Inert or Update)
CALL	Call a PL/SQL program
EXPLAIN PLAN	Explain access path to data
LOCK TABLE	Control concurrency

Some examples are as follows:

GRANT GRANT	Gives user's access privileges to database
REVOKE	Withdraw access privileges given with the GRANT command

TCL statements are used to manage the changes made by DML statements. It allows statements to be grouped together into logical transactions.

COMMIT	Saves work done
SAVEPOINT	Identify a point in a transaction to which you can later roll back
ROLLBACK	Restore database to original since the last COMMIT
SET TRANSACTION	Change transaction options like isolation level and what rollback segment to use.