SQL Query to Update Database
Understanding the Problem
When it comes to updating a database, we often encounter scenarios where we need to update individual rows based on certain conditions. However, in some cases, there might be multiple rows with the same ID, and we want to update only one of them while leaving the others unchanged. In this article, we’ll explore two different solutions to achieve this.
Sample Database
Let’s take a look at our sample database for illustration purposes:
| Id | Name | Address |
|---|---|---|
| 1 | Abc | null |
| 1 | Abc | null |
| 1 | Abc | null |
As you can see, we have three rows with the same ID of 1. We want to update only one of these rows while leaving the others unchanged.
Expectation
Our expected output after updating the database would be:
| Id | Name | Address |
|---|---|---|
| 1 | Abc | xyz |
| 1 | Abc | null |
| 1 | Abc | null |
In this updated database, only one of the rows with ID 1 has been updated to have an Address of ‘xyz’.
Solution 1: Using Rowid
One way to achieve this is by using a rowid function. The rowid function returns the rowid value of each row in the result set.
Here’s the SQL query:
update SAMPLE_DATA_BASE up_d
set up_d.address = 'xyz'
where up_d.rowid in (select first_value(rowid) over (partition by ID)
from SAMPLE_DATA_BASE );
In this query, we’re selecting the rowid value of the first row for each group of rows with the same ID. We then update only those rows based on their rowid values.
Output
After running this query, our database would look like this:
| Id | Name | Address |
|---|---|---|
| 1 | Abc | xyz |
| 1 | Abc | null |
| 1 | Abc | null |
As expected, only one of the rows with ID 1 has been updated to have an Address of ‘xyz’.
Solution 2: Using a New Column
Another way to achieve this is by adding a new column to our table and then updating that column.
Here’s how we can do it:
-- Add a new column to store the row number
alter table SAMPLE_DATA_BASE add (TEMP_ID number);
-- Fill the new column with a different number for each row
update SAMPLE_DATA_BASE set TEMP_ID = rownum;
In this query, we’re adding a new column named ’temp_id’ and filling it with a different number for each row. We then update only one of the rows based on its ’temp_id’ value.
Output
After running these queries, our database would look like this:
| Id | Name | Address | temp_id |
|---|---|---|---|
| 1 | Abc | null | 8 |
| 1 | Abc | xyz | 6 |
| 1 | Abc | null | 7 |
| 9 | Abc | null | 4 |
| 9 | Abc | null | 5 |
| 9 | Abc | asdw | 1 |
| 9 | Abc | xyz | 3 |
| 9 | Abc | null | 2 |
We then update only the row with ’temp_id’ = 1:
-- Update only the row with temp_id = 1
update SAMPLE_DATA_BASE up_d
set up_d.address = 'asdw'
where TEMP_ID = 1;
After running this query, our database would look like this:
| Id | Name | Address | temp_id |
|---|---|---|---|
| 1 | Abc | null | 8 |
| 1 | Abc | xyz | 6 |
| 1 | Abc | null | 7 |
| 9 | Abc | null | 4 |
| 9 | Abc | null | 5 |
| 9 | Abc | asdw | 1 |
| 9 | Abc | xyz | 3 |
| 9 | Abc | null | 2 |
Finally, we drop the new column:
-- Clean up by dropping the temporary column
alter table SAMPLE_DATA_BASE drop column TEMP_ID;
And our database would be back to its original state.
Conclusion
In this article, we explored two different solutions to update a single row in a database while having multiple rows with the same ID. We used both methods of adding a new column and updating that column to achieve the desired result. By understanding how these SQL queries work, you can effectively manage your database updates and maintain data consistency.
Last modified on 2024-09-02