SQL Syntax

Database Tables

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.

Below is an example of a table called "Persons":
P_Id     LastName     FirstName     Address     City
1     Hansen     Ola     Timoteivn 10     Sandnes
2     Svendson     Tove     Borgvn 23     Sandnes
3     Pettersen     Kari     Storgt 20     Stavanger

The table above contains three records (one for each person) and five columns (P_Id, LastName, FirstName, Address, and City).
SQL Statements

Most of the actions you need to perform on a database are done with SQL statements.

The following SQL statement will select all the records in the "Persons" table:
SELECT * FROM Persons

In this tutorial we will teach you all about the different SQL statements.
Keep in Mind That...

    SQL is not case sensitive

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.

We are using MS Access and SQL Server 2000 and we do not have to put a semicolon after each SQL statement, but some database programs force you to use it.
SQL DML and DDL

SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition Language (DDL).

The query and update commands form the DML part of SQL:

    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

The DDL part of SQL permits database tables to be created or deleted. It also defines indexes (keys), specifies links between tables, and imposes constraints between tables. The most important DDL statements in SQL are:

    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