SQL Introduction
What is SQL?
- SQL stands for Structured Query Language. SQL is used to communicate with a database. It is the standard language for relational database management systems.
- Some common relational database management systems that use SQL are Oracle, Sybase, Microsoft SQL Server and Access.
Some of the main purpose of using Oracle SQL:
1. SQL is used to retrieve data from the
database
2. Update data on the database
Standard Commands and its use:
· Data definition language(DDL)
· Data manipulation language(DML)
· Data control language(DCL)
· Transaction control language(TCL)
Data definition language (DDL):
CREATE –To create a
database and its objects like, the create statement used to create a table,
index, views, stored procedure, function, and triggers.
ALTER – Modify or alter the structure of the
existing database
DROP – Delete created 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):
SELECT –
retrieve data from the database
INSERT –
insert data into a table
UPDATE –
updates existing data within a table
DELETE –
Delete all records from a database table
Data control language (DCL):
GRANT –
allow users access privileges to database
REVOKE – withdraw users access privileges given by
using the GRANT command
Transaction control language (TCL):
COMMIT –
commits a Transaction
ROLLBACK –
rollback a transaction because sometimes cause errors
SAVEPOINT – rollback
the transaction making points within groups
SET TRANSACTION –
specify characteristics for the transaction
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