SQL Language Elements and Data type

What is SQL?

SQL is a structure Query language which is used to manage relational database and perform various operations .It is a standardized programming language working on a  various queries such as INSERT,SEARCH, UPDATE, DELETE  database record. It is pronounced as S-Q-L as See-Quel  and it is a standard language for dealing with relational database.

 

SQL Syntax

SELECT* FROM students where age>20

 

Language Elements in SQL

The SQL language is divided into several elements that is  Clauses, Expression, Predicates, Queries and Statements.

Clauses :-  It is a fundamental factor of statement and queries. Clauses are optional for the statements some of the clauses are WHERE clause, HAVING clause.

Expression :-  It is the combination of a value which can produce either scalar value.

Predicates :-  It is used to specify the condition in the SQL that can calculate to SQL . It is used to determine whether something is TRUE or FALSE in expression and change the flow of  the program.

Queries :-  Queries is used to extract the data from the database and present in a readable format. Each query has different function and it is based on a specific criteria.

Statement :-  A statement is a string of characters which have a fixed effect. SQL statement includes semicolon (",")   statement terminator. It controls the flow of program connections, sessions or problems.

 

Data type in SQL

Internal Data TypeDescription
VARCHAR2 (size)Variable length character string having maximum length size bytes.
Maximum size is 2000 and the minimum is 1.
It specify size for a VARCHAR2.
NUMBER (p,s)Number having accuracy a and scale s.
The accuracy a range is about 1 to 38  and the scale s range is about 84 to 127.
LONGVariable length and character data length is uoto 2 gigabytes or 231-1 bytes.
DATAAuthentic data range from January 1,4712 BC to December 31,4712 AD.
RAW (size)Rough binary data of length size bytes.
Maximum size is 255 bytes.
Specify size of RAW value.
LONG RAWRough binary data of variable length up to 2 gigabytes.
ROWIDThis data type is basically used for values return by the ROWID presdocolumn
CHAR (size)Secure length character data of length size byte. 
Maximum size is 255.
Minimum size is 1 byte.

 

SQL Data Definition Language(DDL)

The Data Defination language (DDL) is a part of SQL that allow the database table to create or delete .We can also define keys (index), by establishing  a link between tables, and set the force between the database tables.

There are some most important DDL statements  in SQL are:-

CREATE TABLE
It is used to create a new database table

/*Example*/
CREATE TABLE Student
             (Reg_no varchar2(10),
              Name char(30),
              DOB date,
              Address varchar2(50));


ALTER TABLE
It is used to alters(changes) a database table

/*Syntax*/
ALTER TABLE <table_name>
         ADD (<NewColumnName> <Data_Type>(<size>),......n)


DROP TABLE
It is used to delete a database table

/*Syntax*/
DROP TABLE <table_name>


CREATE INDEX
It is used to create an index (search key)

/*Syntax*/
CREATE INDEX index_name
ON table_name (column1, column2, ...);


DROP INDEX
It is used to delete an index

/*Syntax*/
DROP INDEX <index name>;

 

SQL Data Manipulation Language  (DML)

The SQL language is used for executing queries and it also includes a syntax to insert, update, and  delete records.  These queries and update command from a DML (Data Manipulation Language) which is a part of the SQL .

SELECT
It is used to extract the data from the database table

/*Syntax*/
SELECT * FROM Table_name;

UPDATE
It is used to update the data in a database table

/*Syntax*/
UPDATE tablename

SET col1 = value1, col2 = value2, ...

WHERE criteria

DELETE
It is used to delete the data from the database table

/*Syntax*/
DELETE FROM Table_name;

 


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