Tuesday, August 19, 2014

SQL Syntax

SQL is followed by unique set of rules and guidelines called Syntax. This tutorial gives you a quick start with SQL by listing all the basic SQL Syntax:
All the SQL statements start with any of the keywords like SELECT, INSERT, UPDATE, DELETE, ALTER, DROP, CREATE, USE, SHOW and all the statements end with a semicolon (;).
Important point to be noted is that SQL is case insensitive, which means SELECT and select have same meaning in SQL statements, but MySQL makes difference in table names. So if you are working with MySQL, then you need to give table names as they exist in the database.
All the examples given in this tutorial have been tested with MySQL server.

SQL SELECT Statement:

SELECT column1, column2....columnN
FROM   table_name;

SQL DISTINCT Clause:

SELECT DISTINCT column1, column2....columnN
FROM   table_name;

SQL WHERE Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  CONDITION;

SQL AND/OR Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  CONDITION-1 {AND|OR} CONDITION-2;

SQL IN Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  column_name IN (val-1, val-2,...val-N);

SQL BETWEEN Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  column_name BETWEEN val-1 AND val-2;

SQL LIKE Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  column_name LIKE { PATTERN };

SQL ORDER BY Clause:

SELECT column1, column2....columnN
FROM   table_name
WHERE  CONDITION
ORDER BY column_name {ASC|DESC};

SQL GROUP BY Clause:

SELECT SUM(column_name)
FROM   table_name
WHERE  CONDITION
GROUP BY column_name;

SQL COUNT Clause:

SELECT COUNT(column_name)
FROM   table_name
WHERE  CONDITION;

SQL HAVING Clause:

SELECT SUM(column_name)
FROM   table_name
WHERE  CONDITION
GROUP BY column_name
HAVING (arithematic function condition);

SQL CREATE TABLE Statement:

CREATE TABLE table_name(
column1 datatype,
column2 datatype,
column3 datatype,
.....
columnN datatype,
PRIMARY KEY( one or more columns )
);

SQL DROP TABLE Statement:

DROP TABLE table_name;

SQL CREATE INDEX Statement :

CREATE UNIQUE INDEX index_name
ON table_name ( column1, column2,...columnN);

SQL DROP INDEX Statement :

ALTER TABLE table_name
DROP INDEX index_name;

SQL DESC Statement :

DESC table_name;

SQL TRUNCATE TABLE Statement:

TRUNCATE TABLE table_name;

SQL ALTER TABLE Statement:

ALTER TABLE table_name {ADD|DROP|MODIFY} column_name {data_ype};

SQL ALTER TABLE Statement (Rename) :

ALTER TABLE table_name RENAME TO new_table_name;

SQL INSERT INTO Statement:

INSERT INTO table_name( column1, column2....columnN)
VALUES ( value1, value2....valueN);

SQL UPDATE Statement:

UPDATE table_name
SET column1 = value1, column2 = value2....columnN=valueN
[ WHERE  CONDITION ];

SQL DELETE Statement:

DELETE FROM table_name
WHERE  {CONDITION};

SQL CREATE DATABASE Statement:

CREATE DATABASE database_name;

SQL DROP DATABASE Statement:

DROP DATABASE database_name;

SQL USE Statement:

USE database_name;

SQL COMMIT Statement:

COMMIT;

SQL ROLLBACK Statement:

ROLLBACK;

Intro to RDBMS

What is RDBMS?

RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd.

What is table?

The data in RDBMS is stored in database objects called tables. The table is a collection of related data entries and it consists of columns and rows.
Remember, a table is the most common and simplest form of data storage in a relational database. Following is the example of a CUSTOMERS table:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+

What is field?

Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.
A field is a column in a table that is designed to maintain specific information about every record in the table.

What is record or row?

A record, also called a row of data, is each individual entry that exists in a table. For example there are 7 records in the above CUSTOMERS table. Following is a single row of data or record in the CUSTOMERS table:
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
+----+----------+-----+-----------+----------+
A record is a horizontal entity in a table.

What is column?

A column is a vertical entity in a table that contains all information associated with a specific field in a table.
For example, a column in the CUSTOMERS table is ADDRESS, which represents location description and would consist of the following:
+-----------+
| ADDRESS |
+-----------+
| Ahmedabad |
| Delhi |
| Kota |
| Mumbai |
| Bhopal |
| MP |
| Indore |
+----+------+

What is NULL value?

A NULL value in a table is a value in a field that appears to be blank, which means a field with a NULL value is a field with no value.
It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation.

SQL Constraints:

Constraints are the rules enforced on data columns on table. These are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the database.
Constraints could be column level or table level. Column level constraints are applied only to one column where as table level constraints are applied to the whole table.
Following are commonly used constraints available in SQL:
  • NOT NULL Constraint: Ensures that a column cannot have NULL value.
  • DEFAULT Constraint: Provides a default value for a column when none is specified.
  • UNIQUE Constraint: Ensures that all values in a column are different.
  • PRIMARY Key: Uniquely identified each rows/records in a database table.
  • FOREIGN Key: Uniquely identified a rows/records in any another database table.
  • CHECK Constraint: The CHECK constraint ensures that all values in a column satisfy certain conditions.
  • INDEX: Use to create and retrieve data from the database very quickly.

Data Integrity:

The following categories of the data integrity exist with each RDBMS:
  • Entity Integrity: There are no duplicate rows in a table.
  • Domain Integrity: Enforces valid entries for a given column by restricting the type, the format, or the range of values.
  • Referential integrity: Rows cannot be deleted, which are used by other records.
  • User-Defined Integrity: Enforces some specific business rules that do not fall into entity, domain or referential integrity.

Database Normalization

Database normalization is the process of efficiently organizing data in a database. There are two reasons of the normalization process:
  • Eliminating redundant data, for example, storing the same data in more than one tables.
  • Ensuring data dependencies make sense.
Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored. Normalization consists of a series of guidelines that help guide you in creating a good database structure.
Normalization guidelines are divided into normal forms; think of form as the format or the way a database structure is laid out. The aim of normal forms is to organize the database structure so that it complies with the rules of first normal form, then second normal form, and finally third normal form.
It's your choice to take it further and go to fourth normal form, fifth normal form, and so on, but generally speaking, third normal form is enough.
  • First Normal Form (1NF)
  • Second Normal Form (2NF)
  • Third Normal Form (3NF)

Monday, August 18, 2014

Intro to SQL

SQL is Structured Query Language, which is a computer language for storing, manipulating and retrieving data stored in relational database.
SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server use SQL as standard database language.
Also, they are using different dialects, such as:
  • MS SQL Server using T-SQL,
  • Oracle using PL/SQL,
  • MS Access version of SQL is called JET SQL (native format) etc.

Why SQL?

  • Allows users to access data in relational database management systems.
  • Allows users to describe the data.
  • Allows users to define the data in database and manipulate that data.
  • Allows to embed within other languages using SQL modules, libraries & pre-compilers.
  • Allows users to create and drop databases and tables.
  • Allows users to create view, stored procedure, functions in a database.
  • Allows users to set permissions on tables, procedures, and views

History:

  • 1970 -- Dr. Edgar F. "Ted" Codd of IBM is known as the father of relational databases. He described a relational model for databases.
  • 1974 -- Structured Query Language appeared.
  • 1978 -- IBM worked to develop Codd's ideas and released a product named System/R.
  • 1986 -- IBM developed the first prototype of relational database and standardized by ANSI. The first relational database was released by Relational Software and its later becoming Oracle.

SQL Process:

When you are executing an SQL command for any RDBMS, the system determines the best way to carry out your request and SQL engine figures out how to interpret the task.
There are various components included in the process. These components are Query Dispatcher, Optimization Engines, Classic Query Engine and SQL Query Engine, etc. Classic query engine handles all non-SQL queries but SQL query engine won't handle logical files.
Following is a simple diagram showing SQL Architecture:
SQL Architecture

SQL Commands:

The standard SQL commands to interact with relational databases are CREATE, SELECT, INSERT, UPDATE, DELETE and DROP. These commands can be classified into groups based on their nature:

DDL - Data Definition Language:

CommandDescription
CREATECreates a new table, a view of a table, or other object in database
ALTERModifies an existing database object, such as a table.
DROPDeletes an entire table, a view of a table or other object in the database.

DML - Data Manipulation Language:

CommandDescription
SELECTRetrieves certain records from one or more tables
INSERTCreates a record
UPDATEModifies records
DELETEDeletes records

DCL - Data Control Language:

CommandDescription
GRANTGives a privilege to user
REVOKETakes back privileges granted from user

Introduction to Oracle


ORACLE is a fourth generation relational database management system. In general, a database management system (DBMS) must be able to reliably manage a large amount of data in a multi-user environment so that many users can concurrently access the same data. All this must be accomplished while delivering high performance to the users of the database. A DBMS must also be secure from unauthorized access and provide efficient solutions for failure recovery. The ORACLE Server provides efficient and effective solutions for the major database features.

ORACLE consists of many tools that allow you to create an application with ease and flexibility. You must determine how to implement your requirements using the features available in ORACLE, along with its tools. The features and tools that you choose to use to implement your application can significantly affect the performance of your application.
Several of the more useful features available to ORACLE application developers are integrity constraints, stored procedures and packages, database triggers, cost-based optimizer, shared SQL, locking and sequences.

This documentation will lead you through the main features and tools of ORACLE. It is intended to give you a partial view of what is available to you to use within the assignments.

This documentation will cover:
  • ORACLE Architecture - provides a basic understanding of the ``Big Picture'' including the concepts and terminology of the ORACLE Server. 

  • Starting ORACLE And Other Important Information - provides the knowledge of how to set up your account and other system environment variables. It will also provide information about how ORACLE is currently setup, which you will require, and the steps you must take to report any problems. 

  • SQL*Plus (Terminal Monitor) - provides a summary of the commands that you will require in order to create tables and manipulate the database. 

  • SQL*Loader - provides a summary of the commands that you will require to allow you to load data from a file to the database. 

  • SQL Commands - provides the syntax of some of the SQL Commands in ORACLE to help you get started. This section will only shed light on the Data Definition Language commands and will not contain any information on querying the database (which should be covered in class).