A Gentle Introduction to


Pick an engine:

CIA World Factbook

Some examples of simple WHERE statements:

1 The population of 'France'.

Strings should be in 'single quotes';

2 The names and population densities for the very large countries.

We can use mathematical and string expressions as well as field names and constants.

3 Where to find some very small, very rich countries.

We use AND to ensure that two or more conditions hold true.

4 Which of Ceylon, Iran, Persia and Sri Lanka is the name of a country?

The word IN allows us to check if an item is in a list.

5 What are the countries beginning with D?

The word LIKE permits pattern matching - % is the wildcard.

6 Which countries are not too small and not too big?

BETWEEN allows range checking - note that it is inclusive.

Simple use of SELECT and WHERE

These statements take the form :

SELECT attribute-list
   FROM table-name
   WHERE condition

A common mistake made with boolean expressions

Boolean expressions often read like "normal" English however the syntax is not as rich. For example we might say name equals 'France' or 'Germany' however the corresponding boolean expression is name='France' OR name='Germany'