There are several other scenarios where data needs to be distributed to process. One that comes to mind is count distincts. For example, a count of distinct users or customers like `count(distinct customer_id)` perhaps when doing analysis on purchase transactions. An example SQL might be:

For argument we'll say that purchase_transaction has random distribution. So Netezza has to break up the job. It can't just count distinct on every spu because you can't just add up the numbers at the end because some customers might be on more than one spu. The way to make it where you can just add them up is to make sure a customer can't be on more than one spu, and that means you need the data distributed by customer. That's exactly what the query plan will do, redistribute on customer. But of course if they data is already distributed on customer, then you save having to do a redistribution.

Loading and Unloading Tables

What is a Distribution Key?

In Netezza, a distribution key is a column or combination of columns that determines how data is distributed across the nodes of an appliance. It plays a crucial role in optimizing query performance by minimizing inter-node communication.

Benefits of Using a Distribution Key

Improved query performance: By distributing data based on the distribution key, Netezza can reduce the amount of data that needs to be transferred between nodes, resulting in faster query execution.
Simplified data management: A well-chosen distribution key helps to balance data evenly across all nodes, making it easier to manage and maintain your data warehouse.

Choosing the Right Distribution Key

To choose the right distribution key for your Netezza appliance, consider the following factors:

Choose a column with low cardinality to improve query performance and even data distribution.
Select a column that is correlated with data usage patterns for efficient data distribution and optimized queries.

Example Distribution Key

In this example, we'll create a distribution key for an e-commerce database that tracks customer orders. We'll use the `customer_id` column as our distribution key:

CREATE TABLE orders (
          order_id int,
          customer_id int,
          order_date date,
          ...
        ) WITH (DISTRIBUTION_KEY = 'customer_id');

Common Mistakes to Avoid

Mistake	Consequence
Choosing a column with high cardinality as the distribution key	Uneven data distribution and poor query performance
Using a distribution key that is not correlated with data usage patterns	Inefficient data distribution and queries may not be optimized