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 Northwind sample database (included in MS Access and MS SQL Server).
Below is a selection from the “Customers” table:CustomerIDCustomerNameContactNameAddressCityPostalCodeCountry1
The table above contains five records (one for each customer) and seven columns (CustomerID, CustomerName, ContactName, Address, City, PostalCode, and Country).
Most of the actions you need to perform on a database are done with SQL statements.
The following SQL statement selects all the records in the “Customers” table:
SELECT * FROM Customers;Try it Yourself »
Keep in Mind That…
- SQL keywords are NOT case sensitive:
selectis the same as
In this tutorial we will write all SQL keywords in upper-case.
Semicolon after SQL Statements?
Some database systems require a semicolon at the end of each SQL statement.
Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.
In this tutorial, we will use semicolon at the end of each SQL statement.
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