Join Stage as a Venn Diagram

[John Corbin]

Hi

Saw nothing on this particular question so here goes.

I am to give a lecture/demonstration on the use of a Join Stage to some of our less experienced DS Users.

Start with the basics and show a Left Outer Join.

Can the results of a DataStage Join be shown in a Venn Diagram?

some people learn complex things if a picture can be used to show what is going on.

[ray.wurlod]

Welcome aboard.

The short answer is yes.

A Left Outer Join is the whole of the "left" circle (set), including the intersection with the "right" circle, and nothing else from the "right" circle.

This does not adequately show the substitution of NULL for column values that would have been returned from the "right" set had the join succeeded.

[asorrell]

This is one of my favorite links to use to explain joins - has Venn diagrams as well as data values to illustrate the basic process:

http://www.codinghorror.com/blog/2007/1 ... joins.html

However - please note that these are very simplistic diagrams that ignore some of the subtle aspects of what can occur in a SQL join (especially ones with duplicate key matches).

[John Corbin]

Thanks for the excellent feedback and link.