Handling Custom Query Summation for Groups: A Deep Dive

In this article, we will explore how to handle custom query summation for groups using SQL. We’ll examine a specific use case where you need to group rows based on certain columns and calculate the sum of other columns.

Problem Statement

Let’s consider an example where we have a table named TB1 with the following structure:

The table contains the following data:

Bill.No     Patient_Name       Xray    Price    qty  Doctor
1           Ronny             Test1    100     2   Admin
1           Ronny             Test2    200     3   Admin
2           Mina              Test1    100     2   User
3           Roan              Test4    400     1   Admin
4           Bedo              Test3    50      1   User
4           Bedo              Test3    50      1   User
5           Phill             Test3    50      4   Admin

We need to write a query that groups the rows by Bill.No and calculates the sum of Price and qty for each group. The resulting output should look like this:

Bill.No     Patient_Name       Xray    Price     qty Doctor
1           Ronny        Test1    300     5   Admin
                                Test2         
2           Mina         Test1    100     2   User
3           Roan         Test4    400     1   Admin
4           Bedo         Test3    100     2   User
                                Test3            
5           Phill        Test3    50      4   Admin

The Answer: Using Row Number and Aggregate Functions

The provided answer suggests using the ROW_NUMBER function to achieve this result. Here’s how it works:

SELECT 
  BillNo = CASE WHEN rn = 1 THEN No END,
  Patient_Name = CASE WHEN rn = 1 THEN Patient_Name END,
  Xray,
  Price = CASE WHEN rn = 1 THEN SumPrice END,
  qty = CASE WHEN rn = 1 THEN SumQty END,
  Doctor = CASE WHEN rn = 1 THEN Doctor END
FROM (
    SELECT *,
      rn = ROW_NUMBER() OVER (PARTITION BY Bill.No ORDER BY Xray),
      SumPrice = SUM(Price) OVER (PARTITION BY Bill.No),
      SumQty = SUM(qty) OVER (PARTITION BY Bill.No)
    FROM TB1
) TB1

Let’s break down how this query works:

• We first use the ROW_NUMBER function to assign a unique row number (rn) to each row within each partition of the result set. The rows are partitioned by Bill.No, and the rows are ordered by Xray.
• For each group, we calculate the sum of Price and qty using aggregate functions (SUM). These sums are stored in variables SumPrice and SumQty, respectively.
• We then select the desired columns from the original table (TB1) based on the row number. If the row number is 1, we take the corresponding value for each column.

Understanding the Row Number Function

The ROW_NUMBER function assigns a unique number to each row within a partition of a result set. The rows are ordered by the columns specified in the ORDER BY clause.

Here’s an example to illustrate how ROW_NUMBER works:

Suppose we have the following data:

If we order the rows by Salary in ascending order, ROW_NUMBER will assign row numbers as follows:

In this example, ROW_NUMBER assigns row numbers starting from 1 and incrementing by 1 for each subsequent row.

Handling Custom Query Summation

To handle custom query summation, you can use aggregate functions like SUM, AVG, MAX, MIN, etc. These functions calculate the sum of a column or set of columns in your table.

Here’s an example that demonstrates how to calculate the sum of two columns:

SELECT 
  BillNo,
  Patient_Name,
  Xray,
  SUM(Price) AS PriceSum,
  SUM(qty) AS QtySum
FROM TB1
GROUP BY BillNo, Patient_Name, Xray

In this example, we group the rows by Bill.No, Patient_Name, and Xray and calculate the sum of Price and qty using aggregate functions (SUM). The resulting output will look like this:

Bill.No     Patient_Name       Xray    PriceSum  QtySum
1           Ronny        Test1    300      5
                                Test2         200
2           Mina         Test1    100      2
3           Roan         Test4    400      1
4           Bedo         Test3    100      2
                                Test3          50
5           Phill        Test3    50       4

Conclusion

In this article, we explored how to handle custom query summation for groups using SQL. We examined a specific use case where you need to group rows based on certain columns and calculate the sum of other columns.

We discussed the ROW_NUMBER function, which assigns a unique row number to each row within a partition of a result set. We also demonstrated how to calculate custom query summation using aggregate functions like SUM, AVG, MAX, MIN, etc.

By following the techniques and examples presented in this article, you should be able to handle custom query summation for groups in your SQL queries.

Last modified on 2023-11-16