Table Creation and Display with Conditional Formatting

In this article, we will explore how to create a table that mimics the structure of book pages. We’ll use PostgreSQL as our database management system and provide an example query to achieve the desired output.

Understanding the Problem

Imagine you have a table with page numbers and corresponding titles for recipes. The goal is to display the data in a format that resembles the pages of a book, where even-numbered pages show the title, and odd-numbered pages are blank.

The provided example uses PostgreSQL and attempts to solve this problem using conditional formatting. However, the solution doesn’t quite meet our requirements. In this article, we’ll delve into why the original query fails and provide an alternative approach to achieve the desired output.

Original Query Analysis

Let’s analyze the original query:

SELECT
  CASE WHEN mod (page, 2) = 0 THEN title ELSE 'NULL' END AS even_title,
  CASE WHEN mod (page, 2) &amp; <> 0 THEN title ELSE 'NULL' END AS odd_title
FROM recipes;

The first case statement checks if the page number is divisible by 2. If it is, then the corresponding title is displayed as even_title. Otherwise, 'NULL' is returned.

The second case statement performs a similar check for odd-numbered pages. However, there’s an important distinction: the &amp; <> 0 part of the condition is incorrect. This syntax checks if the result of mod (page, 2) is not equal to 0, which doesn’t make sense in this context.

To fix this, we need to use a different approach that takes into account both even and odd numbers correctly.

Alternative Solution

One way to achieve the desired output is by using the MAX aggregation function with conditional logic. We can group the data by dividing the page number by 2 (since every two consecutive pages form a pair). Then, we use MAX to select the maximum value from each group.

Here’s an alternative query:

SELECT
  max(case when id % 2 = 0 then title else 'NULL' end) as even_page,
  max(case when id % 2 = 1 then title else 'NULL' end) as odd_page
FROM t1  
GROUP BY id / 2
ORDER BY id / 2;

In this query, we use the following steps:

• We group the data by dividing each id by 2. This effectively creates groups for every two consecutive pages.
• For each group, we use max(case when id % 2 = 0 then title else 'NULL' end) to select the maximum value from even-numbered pages (i.e., those where id is divisible by 2).
• Similarly, max(case when id % 2 = 1 then title else 'NULL' end) selects the maximum value from odd-numbered pages.

Final Result

By using this alternative approach, we can achieve the desired output:

This format resembles the pages of a book, where even-numbered pages show the title, and odd-numbered pages are blank.

Conclusion

In this article, we explored how to create a table that mimics the structure of book pages. We analyzed the original query’s limitations and provided an alternative approach using conditional formatting with MAX aggregation. The final result demonstrates how to display data in a format resembling book pages, where even-numbered pages show the title, and odd-numbered pages are blank.

By understanding how to work with PostgreSQL and leveraging the power of aggregations, you can create dynamic tables that adapt to different scenarios. This approach is particularly useful when working with data that requires creative formatting or presentation.

Last modified on 2024-02-08