SQL

SQL:

It stands for "Structured Query Language," and can be called as either "sequel" or "S-Q-L." This is a query language utilized for accessing and modifying information in a database. Some of the common SQL commands include "insert," "update," and "delete." The language was primary created by IBM in the year of 1975 and was called SEQUEL for "Structured English Query Language." whilst then; it has undergone a number of changes, various coming from Oracle products.

Today, SQL is commonly utilized for Web database development and management. Though now SQL is considered to be a standard language, there are till a number of variations of it, such as mSQL and mySQL. Using a scripting language like, PHP, SQL commands can be executed while a Web page loads. It makes it possible to built dynamic Web pages that can display different information each time they load.

What Can SQL do?

  • it can retrieve data through a database
  • it can insert records in a database
  • it can execute queries against a database
  • it can delete records from a database
  • it can update records in a database
  • it can create new tables in a database
  • it can create new databases
  • it can create stored process in a database
  • it can set permissions on tables, procedures, and views.
  • it can create views in a database

Types of SQL:

SQL can be divided in two parts:  first is the Data Manipulation Language (DML) and second is the Data Definition Language (DDL).

DDL:

The DDL part of SQL allows database tables to be created or deleted. This also defines indexes (keys), specifies links among tables, and imposes constraints among tables. The most significant DDL statements in SQL are following:

  • ALTER DATABASE - modifies a database
  • CREATE DATABASE - creates a new database
  • ALTER TABLE - modifies a table
  • CREATE TABLE - creates a new table
  • DROP TABLE - deletes a table
  • CREATE INDEX - creates an index (search key)
  • DROP INDEX - deletes an index

DML:

A data manipulation language (DML) is a family of syntax elements same to a computer programming language utilized for deleting, inserting and updating data in a database. Performing read-only queries of data is sometimes also let a component of DML.

SELECT - extracts data from a database
SELECT column_name(s) FROM table_name

UPDATE - updates data in a database
UPDATE table_name SET column1=value, column2=value2...
WHERE some_column=some_value

DELETE - deletes data from a database
DELETE FROM table_name WHERE some_column=some_value

INSERT INTO - inserts new data into a database
INSERT INTO table_name VALUES (value1, value2, value3,...)

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