Tuesday, 21 July 2015

SQL

http://www.tutorialspoint.com/sql/sql-select-query.htm
SQL is a database computer language designed for the retrieval and management of data in relational database. SQL stands for Structured Query Language.
This tutorial will give you quick start with SQL.

Audience

This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to SQL languages.

Prerequisites

Before you start doing practice with various types of examples given in this reference, I'm making an assumption that you are already aware about what is database, especially RDBMS and what is a computer programming language.

Compile/Execute SQL Programs

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SQL tutorial gives unique learning on Structured Query Language and it helps to make practice on SQL commands which provides immediate results. SQL is a language of database, it includes database creation, deletion, fetching rows and modifying rows etc.
SQL is an ANSI (American National Standards Institute) standard but there are many different versions of the SQL language.

What is 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 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:

Command	Description
CREATE	Creates a new table, a view of a table, or other object in database
ALTER	Modifies an existing database object, such as a table.
DROP	Deletes an entire table, a view of a table or other object in the database.

DML - Data Manipulation Language:

Command	Description
SELECT	Retrieves certain records from one or more tables
INSERT	Creates a record
UPDATE	Modifies records
DELETE	Deletes records

DCL - Data Control Language:

Command	Description
GRANT	Gives a privilege to user
REVOKE	Takes back privileges granted from user

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)

There are many popular RDBMS available to work with. This tutorial gives a brief overview of few most popular RDBMS. This would help you to compare their basic features.

MySQL
MySQL is an open source SQL database, which is developed by Swedish company MySQL AB. MySQL is pronounced "my ess-que-ell," in contrast with SQL, pronounced "sequel."
MySQL is supporting many different platforms including Microsoft Windows, the major Linux distributions, UNIX, and Mac OS X.
MySQL has free and paid versions, depending on its usage (non-commercial/commercial) and features. MySQL comes with a very fast, multi-threaded, multi-user, and robust SQL database server.

History:
Development of MySQL by Michael Widenius & David Axmark beginning in 1994.
First internal release on 23 May 1995.
Windows version was released on 8 January 1998 for Windows 95 and NT.
Version 3.23: beta from June 2000, production release January 2001.
Version 4.0: beta from August 2002, production release March 2003 (unions).
Version 4.01: beta from August 2003, Jyoti adopts MySQL for database tracking.
Version 4.1: beta from June 2004, production release October 2004.
Version 5.0: beta from March 2005, production release October 2005.
Sun Microsystems acquired MySQL AB on 26 February 2008.
Version 5.1: production release 27 November 2008.

Features:

High Performance.
High Availability.
Scalability and Flexibility Run anything.
Robust Transactional Support.
Web and Data Warehouse Strengths.
Strong Data Protection.
Comprehensive Application Development.
Management Ease.
Open Source Freedom and 24 x 7 Support.
Lowest Total Cost of Ownership.

MS SQL Server

MS SQL Server is a Relational Database Management System developed by Microsoft Inc. Its primary query languages are:

T-SQL.
ANSI SQL.

History:

1987 - Sybase releases SQL Server for UNIX.
1988 - Microsoft, Sybase, and Aston-Tate port SQL Server to OS/2.
1989 - Microsoft, Sybase, and Aston-Tate release SQL Server 1.0 for OS/2.
1990 - SQL Server 1.1 is released with support for Windows 3.0 clients.
Aston - Tate drops out of SQL Server development.
2000 - Microsoft releases SQL Server 2000.
2001 - Microsoft releases XML for SQL Server Web Release 1 (download).
2002 - Microsoft releases SQLXML 2.0 (renamed from XML for SQL Server).
2002 - Microsoft releases SQLXML 3.0.
2005 - Microsoft releases SQL Server 2005 on November 7th, 2005.

Features:

High Performance.
High Availability.
Database mirroring.
Database snapshots.
CLR integration.
Service Broker.
DDL triggers.
Ranking functions.
Row version-based isolation levels.
XML integration.
TRY...CATCH.
Database Mail.

ORACLE

It is a very large and multi-user database management system. Oracle is a relational database management system developed by 'Oracle Corporation'.
Oracle works to efficiently manage its resource, a database of information, among the multiple clients requesting and sending data in the network.
It is an excellent database server choice for client/server computing. Oracle supports all major operating systems for both clients and servers, including MSDOS, NetWare, UnixWare, OS/2 and most UNIX flavors.

History:

Oracle began in 1977 and celebrating its 32 wonderful years in the industry (from 1977 to 2009).

1977 - Larry Ellison, Bob Miner and Ed Oates founded Software Development Laboratories to undertake development work.
1979 - Version 2.0 of Oracle was released and it became first commercial relational database and first SQL database. The company changed its name to Relational Software Inc. (RSI).
1981 - RSI started developing tools for Oracle.
1982 - RSI was renamed to Oracle Corporation.
1983 - Oracle released version 3.0, rewritten in C language and ran on multiple platforms.
1984 - Oracle version 4.0 was released. It contained features like concurrency control - multi-version read consistency, etc.
1985 - Oracle version 4.0 was released. It contained features like concurrency control - multi-version read consistency, etc.
2007 - Oracle has released Oracle11g. The new version focused on better partitioning, easy migration etc.

Features:

Concurrency
Read Consistency
Locking Mechanisms
Quiesce Database
Portability
Self-managing database
SQL*Plus
ASM
Scheduler
Resource Manager
Data Warehousing
Materialized views
Bitmap indexes
Table compression
Parallel Execution
Analytic SQL
Data mining
Partitioning

MS ACCESS

This is one of the most popular Microsoft products. Microsoft Access is an entry-level database management software. MS Access database is not only an inexpensive but also powerful database for small-scale projects.
MS Access uses the Jet database engine, which utilizes a specific SQL language dialect (sometimes referred to as Jet SQL).
MS Access comes with the professional edition of MS Office package. MS Access has easy-to-use intuitive graphical interface.

1992 - Access version 1.0 was released.
1993 - Access 1.1 released to improve compatibility with inclusion the Access Basic programming language.
The most significant transition was from Access 97 to Access 2000
2007 - Access 2007, a new database format was introduced ACCDB which supports complex data types such as multi valued and attachment fields.

Features:

Users can create tables, queries, forms and reports and connect them together with macros.
The import and export of data to many formats including Excel, Outlook, ASCII, dBase, Paradox, FoxPro, SQL Server, Oracle, ODBC, etc.
There is also the Jet Database format (MDB or ACCDB in Access 2007), which can contain the application and data in one file. This makes it very convenient to distribute the entire application to another user, who can run it in disconnected environments.
Microsoft Access offers parameterized queries. These queries and Access tables can be referenced from other programs like VB6 and .NET through DAO or ADO.
The desktop editions of Microsoft SQL Server can be used with Access as an alternative to the Jet Database Engine.

Microsoft Access is a file server-based database. Unlike client-server relational database management systems (RDBMS), Microsoft Access does not implement database triggers, stored procedures, or transaction logging.

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:

SQL data type is an attribute that specifies type of data of any object. Each column, variable and expression has related data type in SQL.
You would use these data types while creating your tables. You would choose a particular data type for a table column based on your requirement.
SQL Server offers six categories of data types for your use:

Exact Numeric Data Types:

DATA TYPE	FROM	TO
bigint	-9,223,372,036,854,775,808	9,223,372,036,854,775,807
int	-2,147,483,648	2,147,483,647
smallint	-32,768	32,767
tinyint	0	255
bit	0	1
decimal	-10^38 +1	10^38 -1
numeric	-10^38 +1	10^38 -1
money	-922,337,203,685,477.5808	+922,337,203,685,477.5807
smallmoney	-214,748.3648	+214,748.3647

Approximate Numeric Data Types:

DATA TYPE	FROM	TO
float	-1.79E + 308	1.79E + 308
real	-3.40E + 38	3.40E + 38

Date and Time Data Types:

DATA TYPE	FROM	TO
datetime	Jan 1, 1753	Dec 31, 9999
smalldatetime	Jan 1, 1900	Jun 6, 2079
date	Stores a date like June 30, 1991
time	Stores a time of day like 12:30 P.M.

Note: Here, datetime has 3.33 milliseconds accuracy where as smalldatetime has 1 minute accuracy.

Character Strings Data Types:

DATA TYPE	FROM	TO
char	char	Maximum length of 8,000 characters.( Fixed length non-Unicode characters)
varchar	varchar	Maximum of 8,000 characters.(Variable-length non-Unicode data).
varchar(max)	varchar(max)	Maximum length of 231characters, Variable-length non-Unicode data (SQL Server 2005 only).
text	text	Variable-length non-Unicode data with a maximum length of 2,147,483,647 characters.

Unicode Character Strings Data Types:

DATA TYPE	Description
nchar	Maximum length of 4,000 characters.( Fixed length Unicode)
nvarchar	Maximum length of 4,000 characters.(Variable length Unicode)
nvarchar(max)	Maximum length of 231characters (SQL Server 2005 only).( Variable length Unicode)
ntext	Maximum length of 1,073,741,823 characters. ( Variable length Unicode )

Binary Data Types:

DATA TYPE	Description
binary	Maximum length of 8,000 bytes(Fixed-length binary data )
varbinary	Maximum length of 8,000 bytes.(Variable length binary data)
varbinary(max)	Maximum length of 231 bytes (SQL Server 2005 only). ( Variable length Binary data)
image	Maximum length of 2,147,483,647 bytes. ( Variable length Binary Data)

Misc Data Types:

DATA TYPE	Description
sql_variant	Stores values of various SQL Server-supported data types, except text, ntext, and timestamp.
timestamp	Stores a database-wide unique number that gets updated every time a row gets updated
uniqueidentifier	Stores a globally unique identifier (GUID)
xml	Stores XML data. You can store xml instances in a column or a variable (SQL Server 2005 only).
cursor	Reference to a cursor object
table	Stores a result set for later processing

What is an Operator in SQL?

An operator is a reserved word or a character used primarily in an SQL statement's WHERE clause to perform operation(s), such as comparisons and arithmetic operations.
Operators are used to specify conditions in an SQL statement and to serve as conjunctions for multiple conditions in a statement.

Arithmetic operators
Comparison operators
Logical operators
Operators used to negate conditions

SQL Arithmetic Operators:

Assume variable a holds 10 and variable b holds 20, then:
Show Examples

Operator	Description	Example
+	Addition - Adds values on either side of the operator	a + b will give 30
-	Subtraction - Subtracts right hand operand from left hand operand	a - b will give -10
*	Multiplication - Multiplies values on either side of the operator	a * b will give 200
/	Division - Divides left hand operand by right hand operand	b / a will give 2
%	Modulus - Divides left hand operand by right hand operand and returns remainder	b % a will give 0

SQL Comparison Operators:

Assume variable a holds 10 and variable b holds 20, then:
Show Examples

Operator	Description	Example
=	Checks if the values of two operands are equal or not, if yes then condition becomes true.	(a = b) is not true.
!=	Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.	(a != b) is true.
<>	Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.	(a <> b) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(a > b) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(a < b) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(a >= b) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(a <= b) is true.
!<	Checks if the value of left operand is not less than the value of right operand, if yes then condition becomes true.	(a !< b) is false.
!>	Checks if the value of left operand is not greater than the value of right operand, if yes then condition becomes true.	(a !> b) is true.

SQL Logical Operators:

Here is a list of all the logical operators available in SQL.
Show Examples

Operator	Description
ALL	The ALL operator is used to compare a value to all values in another value set.
AND	The AND operator allows the existence of multiple conditions in an SQL statement's WHERE clause.
ANY	The ANY operator is used to compare a value to any applicable value in the list according to the condition.
BETWEEN	The BETWEEN operator is used to search for values that are within a set of values, given the minimum value and the maximum value.
EXISTS	The EXISTS operator is used to search for the presence of a row in a specified table that meets certain criteria.
IN	The IN operator is used to compare a value to a list of literal values that have been specified.
LIKE	The LIKE operator is used to compare a value to similar values using wildcard operators.
NOT	The NOT operator reverses the meaning of the logical operator with which it is used. Eg: NOT EXISTS, NOT BETWEEN, NOT IN, etc. This is a negate operator.
OR	The OR operator is used to combine multiple conditions in an SQL statement's WHERE clause.
IS NULL	The NULL operator is used to compare a value with a NULL value.
UNIQUE	The UNIQUE operator searches every row of a specified table for uniqueness (no duplicates).

An expression is a combination of one or more values, operators, and SQL functions that evaluate to a value.
SQL EXPRESSIONs are like formulas and they are written in query language. You can also use them to query the database for specific set of data.

Syntax:

Consider the basic syntax of the SELECT statement as follows:

SELECT column1, column2, columnN 
FROM table_name 
WHERE [CONDITION|EXPRESSION];

There are different types of SQL expressions, which are mentioned below:

SQL - Boolean Expressions:

SQL Boolean Expressions fetch the data on the basis of matching single value. Following is the syntax:

SELECT column1, column2, columnN 
FROM table_name 
WHERE SINGLE VALUE MATCHTING EXPRESSION;

Consider the CUSTOMERS table having the following records:

SQL> SELECT * FROM CUSTOMERS;
+----+----------+-----+-----------+----------+
| 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 |
+----+----------+-----+-----------+----------+
7 rows in set (0.00 sec)

Here is simple example showing usage of SQL Boolean Expressions:

SQL> SELECT * FROM CUSTOMERS WHERE SALARY = 10000;
+----+-------+-----+---------+----------+
| ID | NAME  | AGE | ADDRESS | SALARY   |
+----+-------+-----+---------+----------+
|  7 | Muffy |  24 | Indore  | 10000.00 |
+----+-------+-----+---------+----------+
1 row in set (0.00 sec)

SQL - Numeric Expression:

This expression is used to perform any mathematical operation in any query. Following is the syntax:

SELECT numerical_expression as  OPERATION_NAME
[FROM table_name
WHERE CONDITION] ;

Here numerical_expression is used for mathematical expression or any formula. Following is a simple examples showing usage of SQL Numeric Expressions:

SQL> SELECT (15 + 6) AS ADDITION
+----------+
| ADDITION |
+----------+
|       21 |
+----------+
1 row in set (0.00 sec)

There are several built-in functions like avg(), sum(), count(), etc., to perform what is known as aggregate data calculations against a table or a specific table column.

SQL> SELECT COUNT(*) AS "RECORDS" FROM CUSTOMERS; 
+---------+
| RECORDS |
+---------+
|       7 |
+---------+
1 row in set (0.00 sec)

SQL - Date Expressions:

Date Expressions return current system date and time values:

SQL>  SELECT CURRENT_TIMESTAMP;
+---------------------+
| Current_Timestamp   |
+---------------------+
| 2009-11-12 06:40:23 |
+---------------------+
1 row in set (0.00 sec)

Another date expression is as follows:

SQL>  SELECT  GETDATE();;
+-------------------------+
| GETDATE                 |
+-------------------------+
| 2009-10-22 12:07:18.140 |
+-------------------------+
1 row in set (0.00 sec)

The SQL CREATE DATABASE statement is used to create new SQL database.

Syntax:

Basic syntax of CREATE DATABASE statement is as follows:
CREATE DATABASE DatabaseName; Always database name should be unique within the RDBMS.

Example:

The SQL DROP DATABASE statement is used to drop an existing database in SQL schema.

Syntax:

Basic syntax of DROP DATABASE statement is as follows:

DROP DATABASE DatabaseName;

Always database name should be unique within the RDBMS.

Example:

If you want to delete an existing database <testDB>, then DROP DATABASE statement would be as follows:

SQL> DROP DATABASE testDB;

NOTE: Be careful before using this operation because by deleting an existing database would result in loss of complete information stored in the database.
Make sure you have admin privilege before dropping any database. Once a database is dropped, you can check it in the list of databases as follows:

SQL> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| AMROOD             |
| TUTORIALSPOINT     |
| mysql              |
| orig               |
| test               |
+--------------------+
6 rows in set (0.00 sec)

When you have multiple databases in your SQL Schema, then before starting your operation, you would need to select a database where all the operations would be performed.
The SQL USE statement is used to select any existing database in SQL schema.

Syntax:

Basic syntax of USE statement is as follows:
USE DatabaseName; Always database name should be unique within the RDBMS.

Example:

SQL> USE AMROOD;

SQL - CREATE Table

Creating a basic table involves naming the table and defining its columns and each column's data type.
The SQL CREATE TABLE statement is used to create a new table.

Syntax:

Basic syntax of CREATE TABLE statement is as follows:

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

CREATE TABLE is the keyword telling the database system what you want to do. In this case, you want to create a new table. The unique name or identifier for the table follows the CREATE TABLE statement.
Then in brackets comes the list defining each column in the table and what sort of data type it is. The syntax becomes clearer with an example below.
A copy of an existing table can be created using a combination of the CREATE TABLE statement and the SELECT statement. You can check complete details at Create Table Using another Table.

Example:

Following is an example, which creates a CUSTOMERS table with ID as primary key and NOT NULL are the constraints showing that these fields can not be NULL while creating records in this table:

SQL> CREATE TABLE CUSTOMERS(
   ID   INT              NOT NULL,
   NAME VARCHAR (20)     NOT NULL,
   AGE  INT              NOT NULL,
   ADDRESS  CHAR (25) ,
   SALARY   DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

You can verify if your table has been created successfully by looking at the message displayed by the SQL server, otherwise you can use DESC command as follows:

SQL> DESC CUSTOMERS;
+---------+---------------+------+-----+---------+-------+
| Field   | Type          | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ID      | int(11)       | NO   | PRI |         |       |
| NAME    | varchar(20)   | NO   |     |         |       |
| AGE     | int(11)       | NO   |     |         |       |
| ADDRESS | char(25)      | YES  |     | NULL    |       |
| SALARY  | decimal(18,2) | YES  |     | NULL    |       |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

Now, you have CUSTOMERS table available in your database which you can use to store required information related to customers.

SQL - DROP or DELETE Table

The SQL DROP TABLE statement is used to remove a table definition and all data, indexes, triggers, constraints, and permission specifications for that table.
NOTE: You have to be careful while using this command because once a table is deleted then all the information available in the table would also be lost forever.

Syntax:

Basic syntax of DROP TABLE statement is as follows:

DROP TABLE table_name;

Example:

Let us first verify CUSTOMERS table and then we would delete it from the database:

SQL> DESC CUSTOMERS;
+---------+---------------+------+-----+---------+-------+
| Field   | Type          | Null | Key | Default | Extra |
+---------+---------------+------+-----+---------+-------+
| ID      | int(11)       | NO   | PRI |         |       |
| NAME    | varchar(20)   | NO   |     |         |       |
| AGE     | int(11)       | NO   |     |         |       |
| ADDRESS | char(25)      | YES  |     | NULL    |       |
| SALARY  | decimal(18,2) | YES  |     | NULL    |       |
+---------+---------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

This means CUSTOMERS table is available in the database, so let us drop it as follows:

SQL> DROP TABLE CUSTOMERS;
Query OK, 0 rows affected (0.01 sec)

Now, if you would try DESC command, then you would get error as follows:

SQL> DESC CUSTOMERS;
ERROR 1146 (42S02): Table 'TEST.CUSTOMERS' doesn't exist

Here, TEST is database name which we are using for our examples.

SQL - INSERT Query

The SQL INSERT INTO Statement is used to add new rows of data to a table in the database.

Syntax:

There are two basic syntaxes of INSERT INTO statement as follows:

INSERT INTO TABLE_NAME (column1, column2, column3,...columnN)]  
VALUES (value1, value2, value3,...valueN);

Here, column1, column2,...columnN are the names of the columns in the table into which you want to insert data.
You may not need to specify the column(s) name in the SQL query if you are adding values for all the columns of the table. But make sure the order of the values is in the same order as the columns in the table. The SQL INSERT INTO syntax would be as follows:

INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN);

Example:

Following statements would create six records in CUSTOMERS table:

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, 'Ramesh', 32, 'Ahmedabad', 2000.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, 'Khilan', 25, 'Delhi', 1500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (3, 'kaushik', 23, 'Kota', 2000.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (4, 'Chaitali', 25, 'Mumbai', 6500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (5, 'Hardik', 27, 'Bhopal', 8500.00 );


INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (6, 'Komal', 22, 'MP', 4500.00 );

You can create a record in CUSTOMERS table using second syntax as follows:

INSERT INTO CUSTOMERS 
VALUES (7, 'Muffy', 24, 'Indore', 10000.00 );

All the above statements would produce the following records in 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 |
+----+----------+-----+-----------+----------+

Populate one table using another table:

You can populate data into a table through select statement over another table provided another table has a set of fields, which are required to populate first table. Here is the syntax:

INSERT INTO first_table_name [(column1, column2, ... columnN)] 
   SELECT column1, column2, ...columnN 
   FROM second_table_name
   [WHERE condition];

Monday, 20 July 2015

രാമായണം

ഭാരതത്തിന്റെ സംഭാവനയായ രണ്ട് ഇതിഹാസങ്ങളിൽ ഒന്നാണ്‌ രാമായണം .ഇംഗ്ലീഷ്:Ramayana. രാമന്റെ യാത്ര എന്നാണ്‌ രാമായണത്തിനർത്ഥം. വാല്മീകി മഹർഷി രചിച്ച രാമായണം കാവ്യരൂപത്തിലുള്ള ആദ്യ കൃതിയാണ്‌ എന്ന് വിശ്വസിക്കപ്പെടുന്നു. അതുകൊണ്ട് ഇത് ആദിമകാവ്യം എന്നും അറിയപ്പെടുന്നു. മഹത്തായ സീതാചരിത്രവും പൗലസ്ത്യവധവുമാണ് രാമകഥാസംക്ഷേപസാരം. ധാർമ്മികമൂല്യങ്ങളെ മുറുകെ പിടിക്കാനായി മഹത്തായ സിംഹാസനം വരെ ഉപേക്ഷിച്ച രാമനേയും ഭരതനേയും പോലുള്ള മനുഷ്യരുടെ കഥയിലൂടെ മഹത്തരമായ ധർമ്മസം‌രക്ഷണത്തെക്കുറിച്ചുള്ള സന്ദേശമാണ്‌ വാല്മീകിരാമായണത്തിൽ നിന്ന് ലഭിക്കുന്നത്. വാല്മീകിരാമായണത്തിനു മുന്നേ തന്നെ രാമകഥയെ അടിസ്ഥാനമാക്കിയുള്ള ആഖ്യാനങ്ങൾ പ്രചാരത്തിലുണ്ടായിരുന്നു. ആ ആഖ്യാനങ്ങൾ ലഭ്യമല്ലാത്തതിനാലാണ്‌ വാല്മീകിരാമായണം രാമകഥയുടെ ഏറ്റവും പ്രാചീനമായ രൂപമായിത്തീർന്നത്.

മഹാവിജ്ഞനും ബ്രഹ്മർഷിമാരിൽ പ്രധാനിയുമായ വാല്മീകി യുടെ ആശ്രമത്തിൽ വിരുന്നു വന്ന നാരദനോട് വാല്മീകി മഹർഷി 'ധൈര്യം, വീര്യം, ശമം, സത്യവ്രതം, വിജ്ഞാനം, കാരുണ്യം, സൗന്ദര്യം, പ്രൗഢി, ക്ഷമ, ശീലഗുണം, അജയ്യത എന്നീ ഗുണങ്ങൾ ഒത്തുചേർന്ന ഏതെങ്കിലും മനുഷ്യൻ ഭൂമുഖത്തുണ്ടോ എന്ന ചോദ്യം ചോദിക്കുകയും അതിനുത്തരമായി നാരദൻ മഹർഷിക്ക് രാമകഥ വിവരിച്ചുകൊടുക്കുകയും ചെയ്യുന്നിടത്താണ്‌ രാമയണം ആരംഭിക്കുന്നത്. നാരദന്റെ അഭിപ്രായത്തിൽ ശ്രീരാമന്‌ സദൃശ്യനായി മറ്റൊരാളുണ്ടായിരുന്നില്ല.ഗാംഭീര്യത്തിൽ സമുദ്രത്തേയും സൗന്ദര്യത്തിൽ പൂർണ്ണചന്ദ്രനേയും ക്രോധത്തിൽ കാലാഗ്നിയേയും ക്ഷമയിൽ ഭൂമിദേവിയേയും രാമനു സമാനമായി അദ്ദേഹം വിവരിച്ചു. അയോദ്ധ്യയിലെ രാജാവായിരുന്ന ദശരഥമഹാരജാവിന്റെ പട്ടമഹിഷിയായ കൗസല്യയിൽ ഉണ്ടായ ആദ്യപുത്രനാണ്‌ രാമൻ. മറ്റുഭാര്യമാരായ സുമിത്രയിൽ ലക്ഷ്മണനെന്നും കൈകേയിൽ ഭരതനെന്നും മറ്റു പുത്രന്മാരും അദ്ദേഹത്തിനുണ്ടായിരുന്നു. ദശരഥൻ മൂത്തപുത്രനെന്ന നിലയിൽ അനന്തരാവകാശിയായി രാമനെയാണ്‌ കണ്ടിരുന്നത്. പ്രജകളുടെ ഹിതത്തിനനുസരിച്ച് രാമനെ യുവരാജാവായി അഭിഷേകം ചെയ്യാനൊരുങ്ങിയ വേളയിൽ ചില നാടകീയ സംഭവങ്ങൾ ഉണ്ടായി.

തന്റെ മകൻ ഭരതൻ രാജാവാകണമെന്ന് അതിയായി ആഗ്രഹിച്ച കൈകേയി പണ്ടെന്നോ രാജാവ് തനിക്ക് നൽകിയ വരത്തിന്റെ പിൻ‌ബലത്താൽ ഭരതനെ രാജാവാക്കണമെന്നും രാമനെ വാനപ്രസ്ഥത്തിനയക്കണമെന്നും ശഠിച്ചു. സത്യവ്രതനായ ദശരഥപുത്രൻ പിതാവിന്റെ മാനം രക്ഷിക്കാനായി സഹോദരനായ ലക്ഷ്മണനോടും ഭാര്യ സീതയോടും ഒപ്പം യാതൊരു പരിഭവവുമില്ലാതെ വനത്തിലേക്ക് തിരിച്ചു. നിഷാദരാജാവായ ഗുഹൻ അവരെ ഗംഗ കടത്തിവിടുകയും കാട്ടിൽ വച്ച് ഭരദ്വാജമുനിയെ കാണുകയും അദ്ദേഹത്തിന്റെ നിർദ്ദേശപ്രകാരം ചിത്രകൂടത്തിൽ താമസിക്കാനാരംഭിക്കുകയും ചെയ്തു. ആ നാളുകളിൽ ദശരഥൻ ചരമമടഞ്ഞു. യുവരാജാവായി ഭരണം തുടരാൻ ഭരതൻ വിസമ്മതിച്ചു. രാമനെ അന്വേഷിച്ച് ഭരതൻ കാട്ടിലേക്ക് പോകുകയും രാമനെ കണ്ടെത്തുകയും ചെയ്തു. എന്നാൽ ഭരതന്റെ അഭ്യർത്ഥനപ്രകാരം സിംഹാസനത്തിലേക്ക് തിരിച്ചു ചെല്ലാൻ രാമൻ വിസമ്മതിച്ചു. സാന്ത്വനങ്ങളോടെ ഭരതനെ അദ്ദേഹം തിരിച്ചയച്ചു. രാമന്റെ പാദുകങ്ങളെ സ്വീകരിച്ച് അത് മുൻനിർത്തി ഭരതൻ രാജ്യഭാരം നിർവഹിക്കുന്നു.

വീണ്ടും നഗരത്തിൽ നിന്ന് ആളുകൾ എത്തിയെങ്കിലോ എന്ന ആശങ്കകൊണ്ട് രാമൻ കൂടുതൽ ദുർഗ്ഗമമായ ദണ്ഡകാരണ്യത്തിലേക്ക് താമസം മാറ്റി. വിരാധനെന്ന് രാക്ഷസനെ അദ്ദേഹം വധിക്കുന്നു. അഗസ്ത്യമഹർഷിയുടെ ആശ്രമത്തിൽ നിന്ന് ദേവേന്ദ്രന്റെ വില്ലും ബാണങ്ങളൊഴിയാത്ത ആവനാഴിയും അദ്ദേഹം നേടുന്നു. മുനിമാർക്ക് രക്ഷക്കായി രാക്ഷസന്മാരെ വധിക്കാൻ അദ്ദേഹം സഹായിക്കാമെന്നേൽകുന്നു. രാക്ഷസരാജാവായ രാവണന്റെ സഹോദരി ശൂർപ്പണഖയുടെ അംഗഛേദം വരുത്തുന്നത് ഇക്കാലത്താണ്‌. രാവണൻ ശൂർപ്പണഖയുടെ ആഗ്രഹപ്രകാരം പ്രതികാരത്തിനായി പതിനാലായിരം ഘോരരാക്ഷസന്മാരെ അയക്കുന്നു. എന്നാൽ ഇവരെയെല്ലാം രാമൻ എതിർത്ത് തോല്പിക്കുന്നു. മാരീചൻ എന്ന രാക്ഷസന്റെ മായകൊണ്ട് രാവണൻ സീതയെ അപഹരിച്ച് തന്റെ രാജ്യമായ ലങ്കയിലേക്ക് കൊണ്ടുപോകുന്നു. ഇതിനെ തടഞ്ഞ ജടായുവിനെ രാവണൻ വധിച്ചു.

സീതയെ അന്വേഷിച്ചു നടക്കുന്ന രാമലക്ഷ്മണന്മാർ പമ്പാ തീരത്തുവച്ച് ഹനുമാനെ കാണുന്നു. ഹനുമാന്റെ ആഗ്രഹപ്രകാരം സുഗ്രീവനേയും അവർ പരിചയപ്പെടുത്തുന്നു. സുഗ്രീവനെ സ്വന്തം ജ്യേഷ്ഠനായ ബാലിയുടെ നിയന്ത്രണങ്ങളിൽ നിന്ന് മോചിപ്പിച്ച് ബാലിവധം നടത്തുന്നു. പകരമായി സീതയെ അന്വേഷിക്കുന്ന ചുമതല സുഗ്രീവൻ തന്റെ വാനരസേനയെ ഏല്പിക്കുന്നു.

വാനരപ്പടയിൽ പക്ഷിശ്രേഷ്ഠനും ജടായുവിന്റെ സഹോദരനുമായ സമ്പാതിയിൽ നിന്നും ലഭിച്ച വിവരങ്ങളനുസരിച്ച് ഹനുമാൻ നൂറുയോജന വിസ്താരമുള്ള ദക്ഷിണമഹാസമുദ്രം ലംഘിച്ച് ലങ്കയിലെത്തുന്നു. അശോകവനിയിൽ വച്ച് സീതയെ കാണുകയും രാമന്റെ വിശേഷങ്ങൾ അറിയിക്കുകയും ചെയ്ത് രാമന്റെ മുദ്രാമോതിരം കാണിച്ച് വിടവാങ്ങി വരും വഴിക്ക് രാവണനു പിടികൊടുത്ത ഹനുമാന്റെ വാലിനു തീവക്കാൻ രാവണൻ കല്പിക്കുന്നു. വാലിലെ തീയുമായി ഓടിനടന്ന ഹനുമാൻ കൊട്ടാരത്തിനു തീ കൊടുത്ത് നേരമ്പോക്ക് നടത്തുകയും ചെയ്യുന്നു. രാവണന്റെ സേനാപതികളേയും ഇളയമകനായ അക്ഷയകുമാരനേയും ഹനുമാൻ കൊന്നൊടുക്കുന്നു. രാവണനെ വെല്ലുവിളിച്ചശേഷം സമുദ്രം വീണ്ടും തിരിച്ച് ചാടിക്കടന്ന് രാമനടുത്തെത്തി വിവരം അറിയിക്കുന്നു.

രാമൻ യുദ്ധത്തിനുള്ള ഒരുക്കങ്ങൾ ചെയ്ത് സമുദ്രതീരത്തെത്തുന്നു. സേതുബന്ധനം ചെയ്ത് വാനരസേനകളോടൊത്ത് ലങ്കയിലെത്തി യുദ്ധം ചെയ്യുന്നു. യുദ്ധത്തിൽ രാവണനെ വധിക്കുകയും തുടർന്ന് സീതയെ രക്ഷപ്പെടുത്തുകയും ചെയ്യുന്നു. വിഭീഷണനെ രാജാവായി വാഴിച്ചശേഷം രാമൻ തിരിച്ചു പോരുന്നു. സീതയോട് രാമൻ ക്രൂരമായാണ്‌ സംസാരിച്ചത്. എന്നാൽ സീത അഗ്നിയിൽ തന്റെ വിശുദ്ധി തെളിയിച്ച് രാമന്റെ മനസ്സിനെ വിജയിക്കുന്നു.
ശ്രീരാമൻ അയോദ്ധ്യയിൽ വൻ വരവേല്പ് നൽകുകയും അദ്ദേഹം സിംഹാസനാവരോഹണം ചെയ്യുകയും ചെയ്തു. അദ്ദേഹത്തിന്റെ ഭരണകാലത്ത് പ്രജകൾ കൃതയുഗത്തിലെന്ന പോലെ മംഗളകരമായി കഴിഞ്ഞുകൂടി. രോഗങ്ങൾ, ബാലമരണം, വിധവകൾ, പ്രകൃതിക്ഷോഭങ്ങൾ എന്നിവയൊന്നുമില്ലാത്ത രാമരാജ്യം അവർക്ക് ലഭിച്ചു.

Thursday, 16 July 2015

കർക്കടകമാസനാളുകളിൽ...................

കർക്കടകമാസനാളുകളിൽ തലതല്ലിപ്പെയ്യുന്ന മഴമേഘങ്ങൾ. വെള്ളത്തുള്ളികൾ തീർക്കുന്ന മന്ത്രധ്വനി നിറഞ്ഞ സന്ധ്യയിൽ പൂമുഖത്തു തെളിഞ്ഞു കത്തുന്ന നിലവിളക്ക്. അരികിൽ നിവർത്തിപ്പിടിച്ച ആധ്യാത്മ രാമായണവുമായി മുത്തശ്ശി. വീണ്ടുമൊരു രാമായണമാസം എത്തിയിരിക്കുന്നു. രാമനാമത്തിനു മുന്നിൽ യാതനകളില്ല, ആധിയും വ്യാധിയുമില്ല, വിഘ്നങ്ങളും ദുഃഖവുമില്ല. ഇനിയുള്ളതു രാമകഥയുടെ മാഹാത്മ്യം മാത്രം. സർവവും വിശുദ്ധമാക്കുന്ന രാമായണനദിയുടെ പ്രവാഹം മാത്രം.