features and uses of SQL

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Please see the attached file.

SQL

(Structured Query Language) Pronounced "S-Q-L" a language used to interrogate and process data in a relational database. Originally developed by IBM for its mainframes, all database systems designed for client/server environments support SQL. SQL commands can be used to interactively work with a database or can be embedded within a programming language to interface to a database. Programming extensions to SQL have turned it into a full-blown database programming language, and all major database management systems (DBMSs) support the language.

When SQL was not developed File-processing System was very popular for processing and storing the data. But some of the major disadvantages of File-processing System like Data redundancy and inconsistency, difficulty in accessing data, data isolation, concurrent access anomalies lead to the development of SQL.

SQL is a non-procedural language and a language that all commercial RDBMS implementations understand.

Example:
The following SQL query selects customers with credit limits of at least $5,000 and puts them into sequence from highest credit limit to lowest. The bold words are SQL verbs.

select name, city, state, zipcode
from customer
where creditlimit > 4999
order by creditlimit desc

Data Types:
There are various data types that SQL supports like:
Integers

Decimal numbers

Floating point numbers---- FLOAT

Fixed length character strings---- CHAR (len)
Fixed length character data of length len bytes. This should be used for fixed length data.

Variable length character strings --- Varchar2(len)
Variable length character string having maximum length len bytes. We must pecify the size
Dates-----DATE

SQL has three flavors of statements. The DDL, DML and DCL.

DDL is Data Definition Language statements. Some examples:
CREATE - to 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
GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the GRANT command

DML is Data Manipulation Language statements. Some examples:
SELECT - retrieve data from the a database
INSERT - insert data into a table
UPDATE - updates existing data within a table
DELETE - deletes all records from a table, the space for the records remain
CALL - call a PL/SQL or Java subprogram
EXPLAIN PLAN - explain access path to data
LOCK TABLE - control concurrency

DCL is Data Control Language statements. Some examples:
COMMIT - save 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 what rollback segment to use

Set Operational Features:

The SQL operations union, intersect ...