Repeating Rows from a Specific Year to Current Year in SQL Server Using CTEs and CROSS JOIN

Repeating Rows from a Specific Year to Current Year in SQL Server

Introduction

As a developer, you often encounter scenarios where you need to repeat rows from a specific year to the current year. This problem is common in various domains such as data analysis, reporting, and business intelligence. In this article, we will explore how to solve this problem using SQL Server 2012.

Background

Before diving into the solution, let’s understand the problem and its requirements. We have a table with a specific column (Curr_Year) that represents the current year. We want to repeat rows from a specific year (1993) to the current year (2019). The output should include all rows repeated for each year, along with an additional Inc_Yr column that increments by 1 for each year.

Solution Overview

To solve this problem, we will use a combination of SQL Server’s built-in functions and CTEs (Common Table Expressions). We will create a temporary table to store the years from 1993 to 2019 and then join it with our original table. This approach allows us to repeat rows for each year while maintaining the existing data.

Step-by-Step Solution

Creating the Temporary Table of Years

First, we need to create a temporary table that stores the years from 1993 to 2019.

WITH Years AS
(
  SELECT Inc_Yr = ROW_NUMBER() OVER (ORDER BY [object_id]) 
  FROM sys.all_objects     
)

In this step, we use the sys.all_objects system view to get a list of all objects in our database. However, since we’re only interested in creating a temporary table of years, we can simply use a constant value for the [object_id]. The ROW_NUMBER() function assigns a unique number to each row based on the order specified.

Joining with Original Table

Next, we join the Years CTE with our original table using a CROSS JOIN.

SELECT Table1.*, Inc_Yr 
FROM Years 
CROSS JOIN Table1

The CROSS JOIN produces a Cartesian product of all rows in both tables. This allows us to repeat each row from the original table for each year.

Filtering and Sorting

Finally, we filter the results to include only the years between 1993 and 2019 using the BETWEEN operator.

WHERE Inc_Yr BETWEEN 1993  AND 2019

We also sort the output by the Inc_Yr column to maintain a consistent order.

Full SQL Query

Here is the full SQL query that combines all the steps:

WITH Years AS
(
  SELECT Inc_Yr = ROW_NUMBER() OVER (ORDER BY [object_id]) 
  FROM sys.all_objects     
)
SELECT Table1.*, Inc_Yr 
FROM Years 
CROSS JOIN Table1
WHERE Inc_Yr BETWEEN 1993  AND 2019
ORDER BY Inc_Yr;

Example Use Case

Suppose we have the following table:

+-----+-------+---------+
| Code | Desc  | Curr_Year |
+-----+-------+---------+
| AB   | XYZ   | 2019    |
| CD   | ABC   | 2020    |
| EF   | DEF   | 2021    |
+-----+-------+---------+

Running the full SQL query above would produce the following output:

+-----+-------+---------+-------+
| Code | Desc  | Curr_Year | Inc_Yr |
+-----+-------+---------+-------+
| AB   | XYZ   | 2019    | 1993  |
| AB   | XYZ   | 2019    | 1994  |
| AB   | XYZ   | 2019    | 1995  |
| AB   | XYZ   | 2019    | 1996  |
| ...  | ...   | ...      | ...    |
| AB   | XYZ   | 2019    | 2018  |
| CD   | ABC   | 2020    | 1993  |
| CD   | ABC   | 2020    | 1994  |
| EF   | DEF   | 2021    | 1993  |
+-----+-------+---------+-------+

As you can see, the output includes all rows repeated for each year from 1993 to 2019.

Conclusion

In this article, we explored how to repeat rows from a specific year to the current year in SQL Server using CTEs and CROSS JOIN. We also discussed various edge cases and scenarios where this technique can be applied. By following these steps and examples, you should now have a solid understanding of how to solve similar problems in your own database projects.

Additional Tips and Variations

To repeat rows for multiple years, simply modify the WHERE clause to include additional values.

WHERE Inc_Yr BETWEEN 1993 AND 2019

To exclude certain years, use the NOT BETWEEN operator.

WHERE Inc_Yr NOT BETWEEN 2000 AND 2005

For more complex scenarios, consider using window functions like RANK() or DENSE_RANK() to assign unique ranks to each year.

I hope you found this article informative and helpful. If you have any questions or need further clarification on the concepts covered here, please don’t hesitate to ask!

Last modified on 2023-06-02