Quick Guide

What is Database?

A database is a separate application that stores a collection of data. Each database has one or more distinct APIs for creating, accessing, managing, searching, and replicating the data it holds.

Other kinds of data stores can be used, such as files on the file system or large hash tables in memory but data fetching and writing would not be so fast and easy with those type of systems.

So now a days we use relational database management systems (RDBMS) to store and manager huge volume of data. This is called relational database because all the data is stored into different tables and relations are established using primary keys or other keys known as foreign keys.

A Relational DataBase Management System (RDBMS) is a software that:

• Enables you to implement a database with tables, columns, and indexes.
• Guarantees the Referential Integrity between rows of various tables.
• Updates the indexes automatically.
• Interprets an SQL query and combines information from various tables.

RDBMS Terminology:

Before we proceed to explain MySQL database system, lets revise few definitions related to database.

• Database: A database is a collection of tables, with related data.
• Table: A table is a matrix with data. A table in a database looks like a simple spreadsheet.
• Column: One column (data element) contains data of one and the same kind, for example the column postcode.
• Row: A row (= tuple, entry or record) is a group of related data, for example the data of one subscription.
• Redundancy: Storing data twice, redundantly to make the system faster.
• Primary Key: A primary key is unique. A key value can not occur twice in one table. With a key you can find at most one row.
• Foreign Key: A foreign key is the linking pin between two tables.
• Compound Key: A compound key (composite key) is a key that consists of multiple columns, because one column is not sufficiently unique.
• Index: An index in a database resembles an index at the back of a book.
• Referential Integrity: Referential Integrity makes sure that a foreign key value always points to an existing row.

MySQL Database:

MySQL is a fast, easy-to-use RDBMS used being used for many small and big businesses. MySQL is developed, marketed, and supported by MySQL AB, which is a Swedish company. MySQL is becoming so popular because of many good reasons.

• MySQL is released under an open-source license. So you have nothing to pay to use it.
• MySQL is a very powerful program in its own right. It handles a large subset of the functionality of the most expensive and powerful database packages.
• MySQL uses a standard form of the well-known SQL data language.
• MySQL works on many operating systems and with many languages including PHP, PERL, C, C++, JAVA etc.
• MySQL works very quickly and works well even with large data sets.
• MySQL is very friendly to PHP, the most appreciated language for web development.
• MySQL supports large databases, up to 50 million rows or more in a table. The default file size limit for a table is 4GB, but you can increase this (if your operating system can handle it) to a theoretical limit of 8 million terabytes (TB).
• MySQL is customizable. The open source GPL license allows programmers to modify the MySQL software to fit their own specific environments.
  
  
  

  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 uses 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?

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

  History:

  • 1970 -- Dr. E.F. "Ted" 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 digram 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
  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

  DQL - Data Query Language:

  Command	Description
  SELECT	Retrieves certain records from one or more tables

  
  

  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.

  Contraints 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)
    
    
    First normal form (1NF) sets the very basic rules for an organized database:
    • Define the data items required, because they become the columns in a table. Place related data items in a table.
    • Ensure that there are no repeating groups of data.
    • Ensure that there is a primary key.

    First Rule of 1NF:

    You must define the data items. This means looking at the data to be stored, organizing the data into columns, defining what type of data each column contains, and finally putting related columns into their own table.
    For example, you put all the columns relating to locations of meetings in the Location table, those relating to members in the MemberDetails table, and so on.

    Second Rule of 1NF:

    The next step is ensuring that there are no repeating groups of data. Consider we have following table:

    CREATE TABLE CUSTOMERS(
           ID   INT              NOT NULL,
           NAME VARCHAR (20)     NOT NULL,
           AGE  INT              NOT NULL,
           ADDRESS  CHAR (25),
           ORDERS   VARCHAR(155)
    );
    

    So if we populate this table for a single customer having multiple orders then it would be something as follows:

    ID	NAME	AGE	ADDRESS	ORDERS
    100	Sachin	36	Lower West Side	Cannon XL-200
    100	Sachin	36	Lower West Side	Battery XL-200
    100	Sachin	36	Lower West Side	Tripod Large

    But as per 1NF, we need to ensure that there are no repeating groups of data. So let us break above table into to parts and join them using a key as follows:
    CUSTOMERS table:

    CREATE TABLE CUSTOMERS(
           ID   INT              NOT NULL,
           NAME VARCHAR (20)     NOT NULL,
           AGE  INT              NOT NULL,
           ADDRESS  CHAR (25),
           PRIMARY KEY (ID)
    );
    

    This table would have following record:

    ID	NAME	AGE	ADDRESS
    100	Sachin	36	Lower West Side

    ORDERS table:

    CREATE TABLE ORDERS(
           ID   INT              NOT NULL,
           CUSTOMER_ID INT       NOT NULL,
           ORDERS   VARCHAR(155),
           PRIMARY KEY (ID)
    );
    

    This table would have following records:

    ID	CUSTOMER_ID	ORDERS
    10	100	Cannon XL-200
    11	100	Battery XL-200
    12	100	Tripod Large

    Third Rule of 1NF:

    The final rule of the first normal form . create a primary key for each table which we have already created.
    
    
    

    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 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 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
    • 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 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 release to improve compatibility with include the Access Basic programming language.
    • The most significant transition was from the Access 97 to the 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 make difference in table names. So if you are working with MySQL then you need to give table names as they exist in the database.

      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 database_name;

      SQL COMMIT Statement:

      COMMIT;

      SQL ROLLBACK Statement:

      ROLLBACK;.
      
      
      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 value of two operands are equal or not, if yes then condition becomes true.	(a = b) is not true.
    !=	Checks if the value 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 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 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 expression, 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 CUSTOMERS table has 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 examples 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)