SQL Introduction

This tutorial is reworked from the DuckDB tutorial.

Overview

This page provides an overview of how to perform simple operations in SQL. This tutorial is only intended to give you an introduction and is not a complete SQL tutorial.

All queries use the internal sample NASA datasets and should work regardless of what data your installation and setup has access to.

Concepts

Opteryx is a system for querying ad hoc data stored in files as relations. A relation is a mathematical term for a data table.

Each relation is a named collection of rows, organized into columns, where each column should have a common datatype.

As an ad hoc query engine, relations and their schemas do not need to be predefined; they are determined when the query is executed. This is one of the reasons Opteryx cannot be considered an RDBMS (relational database management system), even though it can be used to query data using SQL.

Querying Relations

To retrieve data from a relation, you query it using a SQL SELECT statement. Basic statements consist of three parts: the list of columns to be returned, the list of relations to retrieve data from, and optional clauses to shape and filter the returned data.

sql

SELECT *
  FROM $planets;

The * is shorthand for "all columns". By convention, keywords are capitalized, and ; optionally terminates the query.

sql

SELECT id,
       name
  FROM $planets
 WHERE name = 'Earth';

The output of the above query should be

 id	|  name
----+-------
  3	| Earth

You can write functions, not just simple column references, in the select list. For example, you can write:

sql

SELECT id, 
       UPPER(name) AS uppercase_name
  FROM $planets
 WHERE id = 3;

This should give:

 id	| uppercase_name
----+----------------
  3	| EARTH

Notice how the AS clause is used to relabel the output column. (The AS clause is optional.)

A query can be “qualified” by adding a WHERE clause that specifies which rows are wanted. The WHERE clause contains a Boolean (truth value) expression, and only rows for which the Boolean expression is true are returned. The usual Boolean operators (AND, OR, and NOT) are allowed in the qualification.

The SELECT clause can be thought of as choosing which columns we want from the relation, and the WHERE clause as choosing which rows we want from the relation.

For example, the following query returns planets with fewer than 10 moons and a day longer than 24 hours:

sql

SELECT name,
       length_of_day,
       number_of_moons
  FROM $planets
 WHERE length_of_day > 24
   AND number_of_moons < 10;

Result:

name    | length_of_day | number_of_moons
--------+---------------+-----------------
Mercury |        4222.6 |               0
Venus   |          2802 |               0
Mars    |          24.7 |               2
Pluto   |         153.3 |               5

The order of results is not guaranteed and should not be relied upon. If you request the results of the query below, you might get Mercury or Venus in either order.

Be Aware

The same query, on the same data in the same version of the query engine, will likely return results in the same order. Don't expect to test result order non-determinism by rerunning the query millions of times and looking for differences. These differences may manifest across different versions, or from subtle differences in the query statement or data.

sql

SELECT name,
       number_of_moons
  FROM $planets
 WHERE number_of_moons = 0;

Result:

name    | number_of_moons
--------+-----------------
Mercury |               0
Venus   |               0