To use the row_number() function in Oracle SQL, you simply include it in your SELECT statement along with an OVER clause. The row_number() function assigns a unique sequential integer to each row in the result set based on the order specified in the OVER clause. This can be helpful for ranking or ordering rows in a query result. For example, you can use row_number() to assign a ranking to each row based on a certain column value. The syntax for using row_number() is as follows:

SELECT column1, column2, row_number() OVER (ORDER BY column3) AS row_num FROM table_name;

In this example, row_number() is used to assign a row number to each row in the result set, ordered by the values in column3. You can then use this row_num in your query to filter or order the rows as needed.

## What is the purpose of using row_number() in Oracle SQL?

The purpose of using the row_number() function in Oracle SQL is to assign a unique sequential integer to each row in the result set. This can be helpful in scenarios where you need to identify or rank rows in a specific order, such as determining the top N results or identifying duplicate records.

## What is the default sorting order for row_number() function in Oracle SQL?

The default sorting order for row_number() function in Oracle SQL is ascending order.

## What are the limitations of using row_number() in Oracle SQL?

**Cannot be used in distributed queries**: Row_number() function cannot be used in distributed queries that involve multiple databases or linked servers.**Constant ranking after sorting**: The ranking generated by row_number() function remains constant after sorting and does not adjust automatically if the underlying data changes.**No support for partitions**: Row_number() function does not support partitioning the result set into multiple subsets for ranking.**Performance overhead**: Using row_number() function can introduce performance overhead, especially on large datasets, as it involves assigning a row number to each row in the result set.**Limited flexibility**: As row_number() function assigns a sequential integer to each row in the result set, it may not provide the desired flexibility for ranking based on specific criteria or conditions.

## How to use row_number() in subquery in Oracle SQL?

To use `ROW_NUMBER()`

in a subquery in Oracle SQL, you can follow these steps:

- Write the subquery for which you want to assign row numbers using the ROW_NUMBER() function. For example:

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SELECT employee_id, first_name, last_name, department_id, ROW_NUMBER() OVER (ORDER BY employee_id) AS rn FROM employees |

- Wrap the subquery in another query and filter out the row numbers as needed. For example:

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SELECT * FROM ( SELECT employee_id, first_name, last_name, department_id, ROW_NUMBER() OVER (ORDER BY employee_id) AS rn FROM employees ) subquery WHERE rn <= 10 |

In this example, the subquery assigns row numbers to the employees based on their `employee_id`

, and the outer query filters out the rows where the row number is less than or equal to 10.

You can adjust the `ORDER BY`

clause in the `ROW_NUMBER()`

function and add other conditions in the outer query as needed based on your requirements.

## How to extract specific rows using row_number() in Oracle SQL?

To extract specific rows using the `ROW_NUMBER()`

function in Oracle SQL, you can use a subquery or a Common Table Expression (CTE).

Here is an example using a subquery:

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SELECT * FROM ( SELECT *, ROW_NUMBER() OVER (ORDER BY column_name) AS row_num FROM your_table ) WHERE row_num = specific_row_number; |

In this query:

- your_table is the name of your table.
- column_name is the name of the column you want to order the rows by.
- specific_row_number is the row number you want to extract.

You can modify the `ORDER BY`

clause to define how the rows are ordered. The `ROW_NUMBER()`

function assigns a unique row number to each row based on the order specified.

You can also use a CTE to achieve the same result:

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WITH numbered_rows AS ( SELECT *, ROW_NUMBER() OVER (ORDER BY column_name) AS row_num FROM your_table ) SELECT * FROM numbered_rows WHERE row_num = specific_row_number; |

Using a subquery or CTE allows you to easily retrieve specific rows based on their row numbers using the `ROW_NUMBER()`

function in Oracle SQL.