In SQL Server, the @@FETCH_STATUS function is used to determine the status of the last cursor fetch operation. It is crucial for controlling the flow of cursor operations, particularly within loops that process rows fetched from a cursor.
Here's how to use @@FETCH_STATUS to control the flow of cursor operations:
1. Declare your cursor: Define the cursor with a SELECT statement.
2. Open the cursor: Execute the cursor to process the rows specified in your query.
3. Fetch the first row: Use the FETCH NEXT statement to retrieve the first row into your defined variables.
4. Check @@FETCH_STATUS: After the fetch, you check the value of @@FETCH_STATUS:
- If it is 0, the row was fetched successfully.
- If it is -1, there are no more rows to fetch.
- If it is -2, the row fetched is missing (but this case is uncommon in most cursor scenarios).
5. Process the fetched row: If the fetch was successful, perform your intended operations on the row data.
6. Loop back to fetch the next row: Use a loop (like WHILE) to continue fetching and processing rows until there are no more rows to retrieve (i.e., until @@FETCH_STATUS returns -1).
7. Close and deallocate the cursor: After processing all rows, clean up by closing and deallocating the cursor.
Here's a simple example to demonstrate the flow using a cursor:
DECLARE @SomeColumn INT;
-- Step 1: Declare the cursor
DECLARE MyCursor CURSOR FOR
SELECT SomeColumn FROM SomeTable;
-- Step 2: Open the cursor
OPEN MyCursor;
-- Step 3: Fetch the first row
FETCH NEXT FROM MyCursor INTO @SomeColumn;
-- Step 4: Loop through the rows
WHILE @@FETCH_STATUS = 0
BEGIN
-- Process each row
PRINT @SomeColumn;
-- Step 5: Fetch the next row
FETCH NEXT FROM MyCursor INTO @SomeColumn;
END;
-- Step 6: Close the cursor
CLOSE MyCursor;
-- Step 7: Deallocate the cursor
DEALLOCATE MyCursor;
In this example:
- A cursor named MyCursor is declared to select SomeColumn from SomeTable.
- The first row is fetched, and if successful, it prints the value.
- The loop continues to fetch and process rows as long as @@FETCH_STATUS returns 0.
- Finally, the cursor is closed and deallocated to free resources.
By checking the @@FETCH_STATUS after each fetch, you ensure the loop exits when there are no more rows to process, effectively controlling the flow of the cursor operations.