SQL is a database computer language designed for the retrieval and management of data in relational database. SQL stands for Structured Query Language.
SQL- Structured Query Language is a special-purpose programming language designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS).
SQL is used to communicate with a database. According to ANSI (American National Standards Institute), it is the standard language for relational database management systems. SQL statements are used to perform tasks such as update data on a database, or retrieve data from a database. Some common relational database management systems that use SQL are: Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc.
SQL was one of the first commercial languages for Code’s relational model, as described in his influential 1970 paper, “A Relational Model of Data for Large Shared Data Banks.”. Despite not entirely adhering to the relational model as described by Codd, it became the most widely used database language.
The standard SQL commands such as “Select”, “Insert”, “Update”, “Delete”, “Create”, and “Drop” can be used to accomplish almost everything that one needs to do with a database. This tutorial will provide you with the instruction on the basics of each of these commands as well as allow you to put them to practice using the SQL Interpreter.
A database most often contains one or more tables. Each table is identified by a name (e.g. “Customers” or “Orders”). Tables contain records (rows) with data.
In this tutorial we will use the well-known North wind sample database (included in MS Access and MS SQL Server).
For example, to display data from database, select command is used,
SELECT * FROM Customers;
The most common operation in SQL, the query, makes use of the declarative SELECT statement. SELECT retrieves data from one or more tables, or expressions. Standard SELECT statements have no persistent effects on the database. Some non-standard implementations of SELECT can have persistent effects, such as the SELECT INTO syntax provided in some databases.
SQL keywords are NOT case sensitive like any other c language: select is the same as SELECT
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
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