sql

Seite 1

SQL

3

DDL

-

Data Definition Language

Command

Description

CREATE

Creates a new table, a view of a table, or other object in

the

database

.

ALTER

Modifies an existing database object, such as a table.

DROP

Deletes an entire table, a view of a ta

ble or other object

s

in the

database.

DML

-

Data Manipulation Language

Command

Description

SELECT

Retrieves certain records from one or more tables

.

INSERT

Creates a record

.

UPDATE

Modifies records

.

DELETE

Deletes records

DML is abbreviation of Data Manipulation

Language. It is used to retrieve, store, modify, delete, insert and

update data in database. DDL is abbreviation of Data Definition Language. It is used to create and modify the structure of database objects in database.

Delete: The DELETE command is used to

remove rows from a table. A WHERE

clause can be used to only remove some

rows. If no WHERE condition is

specified, all rows will be removed.

After performing a DELETE operation

you need to COMMIT or ROLLBACK the

transaction to make the change

permanent or to undo it. Note that

this operation will cause all DELETE

triggers on the table to fire.

Drop: The DROP command removes a table

from the database. All the tables'

rows, indexes and privileges will also

be removed. No DML triggers will be

fired. The operation cannot be rolled

back