SQL (Structured Query
- Simpel Query Language) is the standard language
for accessing databases. Knowledge of SQL is invaluable for anyone
wanting to interact (store, retrieve, manipulate) data from a
database. Using of a good SQL tool like SQL*XL allows
the user to interact with the data in the database.
Although SQL is an ANSI standard different dialects exist for the
different database types. There is specific Oracle, SQL Server,
Access, ... syntax. The basic statements are the same luckily.
SQL Data Query Language (DQL)
Using DQL data is
retrieved from tables in the database. This is done through a so
called SELECT statement in which we indicate what should be
retrieved from which table.
SELECT * from
This statement retrieves all rows and all columns
from the Customers table.
SELECT cust_id, cust_name from
Customers where cust_town = 'NEW YORK';
This statement retrieves
the id and name for all customers from New York.
SQL Data Manipulation Language (DML)
Using DML data in
a database is added, altered or deleted. Using an INSERT statement a
row is added to a table. An UPDATE statement is used to modify the
data in a row and the DELETE statement is used to remove a row.
SQL Data Definition Language (DDL)
Using DDL database
objects can be created, altered or deleted. Using a CREATE TABLE
statement a table can be created. Deleting a table is done using the
DROP TABLE statement. Similarly views and other database objects can
be created and deleted.
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