what is SQL? let`s get easy full knoweledge and notes.

              

• what is SQL?
  

SQL is stands for structured query language. According to ANSI(  american national standard institutes) in 1986.It is the standard language for relational database management system .
basically sql stands for sturctured query language is a database management language relational database.
sql  isn`t a programming language ,its a query language.
some common relational database management system  that use sql are : Oracle , sybase ,microsoft sql server etc.
The standard  sql commands such as "select","Insert","Update"," Delete","Create","Drop" can be used to accomplish almost everything that one needs to do with a database.

   
                               Every table is divided into smaller entities called fields. The fields in the Customers table consist of CustomerID, CustomerName, ContactName, Address, City, PostalCode and Country. A field is a column in a table that is designed to maintain specific information about every record in the table.

A record, also called a row, is each individual entry that exists in a table. For example, there are 91 records in the above Customers table. A record is a horizontal entity in a table.

• Uses of SQL:-
  

1. SQL is used to communicate with a databse.
2. sql statements are used to performs tasks such as update data on a database.
3. Retrieve data from a database .
4. SQL lets you access and manipulate database.
5. sql can create views in a database.
6. sql can set permission on tables procedures and users.

• Data Definition language (DDL):- :- 

The SQL-DDL contains set of commands, which sets up , chnages or removes/delete data sturctures from the database. These data structures can be tables or pther database objects.

• Data manipulation language(DML):-

The SQL-DML includes those commands , which are based on both the relational algebra and the tuple relational calculus . DML is a language that enales users to access or manipulate data. By data manipulation ,we mean:

1. The retrieval of information stored in the table .
   
2. The insertion of new rows with information into the table.
3. The modification of information stored into the table.
   

• DCL:-   Data control language.
• TCL:- Trasaction control language.  
  

• Data types :-

1.DECIMAL and NUMERIC :-   

   Fixed precision and decimal numbers ,DECIMAL and NUMERIC are functionally equivalent .

syntax:

DECIMAL ( precision [  ,  scale ] )

NUMERIC ( precision [  ,  scale ] )

examples:-

SELECT CAST ( 123 AS DECIMAL (5,2 ) ) - - returns 123.00

SELECT CAST ( 12345.12 AS NUMERIC ( 10,5 0) - - returns  3 . 141593

2. FLOAT  and REAL:-

Approximate number datatypes for use with floating point numeric data.

SELECT CAST (  (PI ( )  AS FLOAT ) --return 3.14159265358979

SELECT CAST ( ( PI ( )  AS REAL ) -- returns 3.141593

3. INTEGERS:-

Exact number data types that use integer data.

Data type                                   Range                                   Storage

bigint       -2^63 (-9,223,372,036,854,775,808) to

                 2^63-1 (9,223,372,036,854,775,807)                  8bytes

int              -2^31 (-2,147,483,648) to 2^31-1

                  (2,147,483,647)                                                    4bytes                     

smallint    -2^15 (-32,768) to 2^15-1 (32,767)                      2bytes

tinyint       0 to 255                                                                   1bytes

4. MONEY and SMALLMONEY :-

Datatypes that represent monetary and currency value.

Data type                                             Range                                  Storage

money                      -922,337,203,685,4775808 to

                                 922337,203,685,477,5807                         8bytes

smallmoney          -214,748.3648 to 214,748.3648                   4bytes

5 .BINARY and VARBINARY:- 

Binary datatype either fixed length or variable length.

Syntax:-

BINARY [ ( n_bytes) ]

VARBINARY [ ( n_bytes  |  max  ) ]

n_bytes can be any number fro 1 to 8000  bytes. max indicates that the max storage space  is 2^31-1.

examples:-

SELECT CAST (12345 AS BINARY( 10 ) ) -- 0X000000000000000000003039

SELECT CAST ( 12345 AS VARBINARY ( 10 ) ) - - 0X00003039

 6.CHAR and VARCHAR:- 

String datatypes of either fixed lenght or variable lenght.

syntax:-

CHAR  [  (  n_chars  )  ]

VARCHAR  [ ( n_chars  )  ]

7.NCHAR and  NVARCHAR:-

UNICODE String datatypes of either fixed lenght or variable lenght.

syntax :

NCHAR  [  ( n_chars  )  ]

NVARCHAR  [  ( n_chars |  MAX  )  ]

use MAX for very long string that may exceed 8000 characters .

• Some of The Most Important SQL Commands:-

• SELECT - extracts data from a database
• UPDATE - updates data in a database
• DELETE - deletes data from a database
• INSERT INTO - inserts new data into a database
• CREATE DATABASE - creates a new database
• ALTER DATABASE - modifies a database
• CREATE TABLE - creates a new table
• ALTER TABLE - modifies a table
• DROP TABLE - deletes a table
• CREATE INDEX - creates an index (search key)
• DROP INDEX - deletes an index

•  Statements of SQL:-
  

Mostly the actions are perform on a database are done with SQL statements.

 so the following SQL statement selects all the records in the "Customers" table:

Example

SELECT * FROM Customers;  

• Remember That...

• SQL keywords are NOT case sensitive: select is the same as SELECT

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• Semicolon after  the SQL Statements:--

Some database systems need a semicolon at the end of each SQL statement.

Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.