What is SQL?
SQL stands for Structured Query Language
SQL is a standard language for accessing databases
SQL has been an international standard (ISO) since 1987
SQL Statements
To access a database, you use SQL statements.
The following SQL statement selects all records in a database table called "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:
- CustomerID (ID)
- CustomerName
- ContactName
- Address
- City
- PostalCode
- 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
Full SQL Tutorial
This has been a short introduction to SQL.
For a full SQL tutorial go to W3Schools SQL Tutorial.
