A Brief Introduction to kdb+

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Contents

Introduction

kdb+ is a powerful database that can be used for streaming, real-time and historical data. q is the SQL-like general purpose programming language built on top of kdb+ that offers high-performance, in-database analytic capabilities.

Installation

The kdb+ 32-bit trial version can be downloaded from the Kx website. See Installation for a step-by-step guide on installing kdb+.

Starting kdb+

At the shell prompt, type q to start a q console session where the prompt q) will appear.

bash$q
q)

Creating a table

To begin learning q/kdb+ we will create a simple table. To do this please type or copy the below code into your q session. Please ensure to remove the leading q) from these code snippets.

q)n:1000000;
q)item:`apple`banana`orange`pear;
q)city:`beijing`chicago`london`paris;
q)tab:([]time:asc n?0D0;n?item;amount:n?100;n?city);

This code creates a table called tab which contains 1 million rows and 4 columns of random time-series sales data. For now, understanding these line of code is not important.

Simple Query

The first query we run selects all rows from the table where the item sold is a banana.

q)select from tab where item=`banana                                            
time                 item   amount city   
------------------------------------------
0D00:00:00.466201454 banana 31     london 
0D00:00:00.712388008 banana 86     london 
0D00:00:00.952962040 banana 20     london 
0D00:00:01.036425679 banana 49     chicago
0D00:00:01.254006475 banana 94     beijing
..

Please note that all columns in the table are returned in the result when there is no column explicitly mentioned.

Aggregate Query

The next query will calculate the sum of the amounts sold of all items by each city.

q)select sum amount by city from tab                                            
city   | amount  
-------| --------
beijing| 12398569
chicago| 12317015
london | 12375412
paris  | 12421447

This uses the aggregate function sum within the q language. Please note that this returns a keyed table where the key column is city. This key column is returned in alphabetical order automatically by kdb+.

Time-Series Aggregate Query

The following query shows the sum of the amount of each item sold by hour during the day.

q)select sum amount by time.hh,item from tab                                    
hh item  | amount
---------| ------
0  apple | 522704
0  banana| 506947
0  orange| 503054
0  pear  | 515212
1  apple | 513723
..

The result is a keyed table with two key columns, hh for the hour and item. The results are ordered by the keyed columns. This query extracts the hour portion from the nanosecond-precision time column by adding a .hh to the column name.

Congratulations, you have now successfully created and queried your first kdb+ table!

What's Next?

Have a look at some more complex in-memory queries.

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