Duplicate Row Based on Column Value

In this article, we will explore how to duplicate a row in a database table based on the value of a specific column. We’ll use SQL Server as our example database management system and provide a step-by-step guide on how to achieve this.

Background

The problem of duplicating rows is common in data processing and analysis. It can be useful for creating backup copies, testing scenarios, or even simply making a table more interesting by repeating certain values.

However, when dealing with tables that contain multiple values in one column, it becomes more complex. In our example, we’ll use the TestData table, which contains four columns: Data1, Data2, Data3, and Data4. The value of Data4 will be used to duplicate rows.

Understanding the Problem

Let’s take a look at the original data in the TestData table:

We want to duplicate the row where Data4 contains multiple values. This means we’ll create a new table that will have the same value for Data1, Data2, and Data3, but with an additional column containing the duplicated values.

Step-by-Step Solution

To achieve this, we’ll use a combination of SQL Server’s CREATE TABLE statement, INSERT INTO statements, and some clever uses of string manipulation functions like CHARINDEX and STUFF.

Creating the Original Table

First, let’s create the original table with some sample data:

-- Create the table
create table TestData(Data1 varchar(50), Data2 varchar(50), Data3 int, Data4 varchar(max))

-- Insert sample data
insert into TestData select 'A', 'E', '9', 'I76J-I76H-I76I-I76G'
insert into TestData select 'B', 'F', '8', 'I76J-I76H-I76I'
insert into TestData select 'C', 'G', '7', 'I76J-I76H'
insert into TestData select 'D', 'H', '6', 'I76J'

Duplicating the Row

Now, let’s create a temporary table that will contain the duplicated values. We’ll use the CHARINDEX function to find the position of the first hyphen (-) in the value of Data4.

-- Create a temporary table with the duplicated values
with tmp(Data1, Data2, Data3, DataItem, Data4) as (
    -- Select the original data
    select Data1, Data2, Data3, LEFT(Data4, CHARINDEX('-',Data4+'-')-1),
        STUFF(Data4, 1, CHARINDEX('-',Data4+'-'), '')
    from TestData
    union all
    -- Select the duplicated values
    select Data1, Data2, Data3, LEFT(Data4, CHARINDEX('-',Data4+'-')-1),
        STUFF(Data4, 1, CHARINDEX('-',Data4+'-'), '')
    from tmp
    where Data4 > ''
)

In this code snippet:

• We use the CHARINDEX function to find the position of the first hyphen (-) in the value of Data4. This will be used as a separator between the original values and the duplicated values.
• We use the STUFF function to remove any remaining hyphens from the value of Data4 before inserting it into the temporary table.

Inserting the Duplicated Data

Now that we have our temporary table with the duplicated values, let’s insert them into the original table:

-- Insert the duplicated data into the original table
insert into TestData
select Data1, Data2, Data3, DataItem AS Data4
from tmp
order by Data1

Deleting the Original Data

Before we can see our results, let’s delete the original values from Data4:

-- Delete the original data from Data4
delete from TestData
where Data4 like '%-%'

Verifying the Results

Finally, let’s verify that our duplicated rows have been successfully inserted into the table:

-- Select the results
select * FROM TestData

This will display the following output:

As we can see, the duplicated rows have been successfully inserted into the table.

Conclusion

In this article, we explored how to duplicate a row in a database table based on the value of a specific column. We used SQL Server as our example database management system and provided step-by-step instructions for achieving this task using clever uses of string manipulation functions like CHARINDEX and STUFF.

Last modified on 2023-06-29