Concatenating Distinct Strings and Numbers

In this article, we will explore how to concatenate distinct strings and numbers from a database table while avoiding duplicate sums.

Background

Let’s consider an example where we have a table emp with columns for employee name, ID, and allowance. We want to create a report that shows the distinct concatenated IDs of employees along with their total allowances.

CREATE TABLE emp (
  name VARCHAR2(100) NOT NULL,
  employee_id VARCHAR2(100) NOT NULL,
  employee_allowance NUMBER NOT NULL
);

INSERT INTO emp (name, employee_id, employee_allowance)
VALUES ('Bob', '11Bob923', 13),
       ('Bob', '11Bob532', 13),
       ('Sara', '12Sara833', 93),
       ('John', '18John243', 21),
       ('John', '18John243', 21),
       ('John', '18John823', 43);

Problem Statement

Suppose we have the following data in our emp table:

We want to create a report that shows the distinct concatenated IDs of employees along with their total allowances. However, we do not want to sum up the duplicate allowance for each employee ID.

Initial Attempt

Our initial attempt at solving this problem is:

SELECT
  name,
  LISTAGG(DISTINCT employee_id, ', ') WITHIN GROUP (ORDER BY employee_id) "ids",
  SUM(employee_allowance)
FROM emp
GROUP BY name;

However, this query still sums up the duplicate allowance for each employee ID. We need to find a way to avoid these duplicates.

Solution

To solve this problem, we can first find the distinct rows in our table using the DISTINCT keyword and then aggregate the results. Here’s how we can do it:

SELECT name,
       LISTAGG(employee_id, ', ')  WITHIN GROUP (ORDER BY employee_id) AS employee_ids,
       SUM(employee_allowance) AS allowance
FROM (
  SELECT DISTINCT *
  FROM emp
)
GROUP BY name;

This query works as follows:

1. The subquery SELECT DISTINCT * FROM emp finds all distinct rows in the table.
2. The outer query aggregates these distinct rows using the LISTAGG function to concatenate the employee IDs and the SUM function to calculate the total allowance.
3. The results are grouped by the employee name.

The output of this query is:

As we can see, the duplicate allowance for each employee ID has been avoided.

Explanation

The key to this solution is using the DISTINCT keyword in the subquery to find all distinct rows in the table. This ensures that we are working with a set of unique data points, rather than duplicates.

Next, we use the LISTAGG function to concatenate the employee IDs within each group. The WITHIN GROUP (ORDER BY employee_id) clause specifies that we want to order the IDs by their original order in the table.

Finally, we use the SUM function to calculate the total allowance for each group.

Conclusion

In this article, we explored how to concatenate distinct strings and numbers from a database table while avoiding duplicate sums. We used the DISTINCT keyword to find all distinct rows in the table and then aggregated the results using the LISTAGG function and the SUM function. The output of our query shows that the duplicate allowance for each employee ID has been avoided.

Additional Considerations

There are several additional considerations when working with data in SQL:

• Data Integrity: When working with large datasets, it’s essential to ensure that your queries are correctly formatted and that you’re using proper join techniques.
• Performance Optimization: Optimizing the performance of your queries can significantly improve the speed at which your application processes data. This may involve reorganizing your tables, indexing columns, or applying other optimization techniques.
• Error Handling: When working with complex queries, it’s essential to include error handling mechanisms to catch any unexpected errors that may occur.

By following these best practices and using techniques like the one presented in this article, you can build robust and efficient SQL queries that meet your application’s needs.

Last modified on 2024-02-27