What is Cursor in SQL ?

Cover Image Of What is Cursor in SQL ?

In SQL, a cursor is a database object used to retrieve and manipulate data row by row. It provides a way to iterate over a result set returned by a SQL query, allowing you to process each row individually. Cursors are particularly useful when you need to perform complex data manipulation or processing tasks that cannot be easily achieved using standard SQL commands.

Here's a basic overview of how cursors work:

1. Declare Cursor: 

You start by declaring a cursor, specifying the SELECT statement that defines the result set to be processed.

2. Open Cursor: 

After declaring the cursor, you open it to execute the associated SELECT statement and populate the result set.

3. Fetch Rows: 

Once the cursor is open, you can fetch rows from the result set one at a time using the FETCH statement. This allows you to process each row individually.

4. Process Data: 

You can perform various operations on each row fetched from the cursor, such as reading values, updating data, or performing calculations.

5. Close Cursor: 

After you have finished processing the result set, you close the cursor to release associated resources and free up memory.

Here's a simple example of using a cursor in SQL:

In this example:

 We declare a cursor named `cursor_name` for a SELECT statement that retrieves data from `table_name`.

 We open the cursor to execute the SELECT statement.

 We fetch each row from the cursor into variables `@variable1` and `@variable2`, process them, and then fetch the next row until there are no more rows to fetch.

 Finally, we close and deallocate the cursor.

Cursors can be useful in certain scenarios, but they should be used judiciously as they can impact performance and may not always be the most efficient solution.