In this article, we will delve into the process of creating views in Netezza, a high-performance data warehouse database system. Views serve as virtual tables based on the result-set of an SQL statement. They can simplify complex queries, enhance security, and promote better organization of your database schema.
The fundamental syntax for creating a view in Netezza is as follows:
CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;
Consider a table named `sales` with columns `region`, `product`, and `amount`. To create a view that displays the total sales for each region, we can employ the following SQL statement:
CREATE VIEW total_sales AS
SELECT region, SUM(amount) as total_sales
FROM sales
GROUP BY region;
Suppose we have another table named `customers` with columns `region`, `customer_name`, and let's see the top 5 customers in each region. We can create a view that joins both tables:
CREATE VIEW top_5_customers AS
SELECT region, customer_name, amount
FROM sales
JOIN customers ON sales.region = customers.region
WHERE rownum <= 5
GROUP BY region, customer_name;
Netezza does not support the `AS` keyword when renaming columns in a view. Instead, you should use a subquery to achieve column renames:
CREATE VIEW sales_view AS
SELECT region, product, SUM(amount) as total_sales_per_product
FROM sales
GROUP BY region, product;
-- To query the view and rename columns:
SELECT region, product as item, total_sales_per_product as sales
FROM sales_view;
If you alter or change the underlying view table, the view becomes obsolete and unusable until you re-compile it. IBM has provided a script to check if a view is obsolete. The general location of this script is /nz/support/bin, but you should consult your Netezza admin team for the exact location. Below is the script and its usage:
nz_check_views [database] [-replace ]