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What is SQL

What is SQL

đź‘‹ Introduction

SQL is a standard language for accessing databases

SQL stands for Structured Query Language

SQL has been an international standard (ISO) since 1987

It is popular and used in many roles in different industries. 

Example of roles that uses SQL:

  • Business Analysts
  • Researchers and scientists
  • Database administrators
  • Data Scientists
  • Developers

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SQL Statements

To access a database, you use SQL statements.

The following SQL statement selects all records in a database table called "Customers":


SELECT * FROM Customers;

Database Tables

A database most often contains one or more tables.

Each table is identified by a name like "Customers" or "Orders".


Below is a selection from a "Customers" table:

ID CustomerName ContactName Address City PostalCode Country
1  Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2  Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3  Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4  Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5  Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden


The table above contains five records (one for each customer) and seven columns:

  1. CustomerID (ID)
  2. CustomerName
  3. ContactName
  4. Address
  5. City
  6. PostalCode
  7. Country

The Most Important SQL Statements:

  • 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

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


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