Slide 14.6: SQL (Structured Query Language)

SQL (Structured Query Language)

LastName	FirstName	Address	City
Hansen	Ola	Timoteivn 10	Sandnes
Svendson	Tove	Borgvn 23	Sandnes
Pettersen	Kari	Storgt 20	Stavanger

SQL Queries
With SQL, we can query a database and have a result set returned.

 SELECT  LastName  FROM  Persons;

==>

LastName
Hansen
Svendson
Pettersen

SQL Data Manipulation Language (DML)
SQL is a syntax for executing queries. But the SQL language also includes a syntax to update, insert, and delete records. These query and update commands together form the DML part of SQL:

SELECT—extracts data from a database table.
UPDATE—updates data in a database table.
DELETE—deletes data from a database table.
INSERT INTO—inserts new data into a database table.

SQL Data Definition Language (DDL)
The Data Definition Language (DDL) part of SQL permits database tables to be created or deleted. We can also define indexes (keys), specify links between tables, and impose constraints between database tables. The most important DDL statements in SQL are

CREATE TABLE—creates a new database table.
ALTER TABLE—alters (changes) a database table.
DROP TABLE—deletes a database table.
CREATE INDEX—creates an index (search key).
DROP INDEX—deletes an index.