How do I loop through a set of records in SQL Server?

sql

set-based-operations

performance-optimization

database-management

byNikita Barsukov·Oct 24, 2024

Here's a quick HOWTO for iterating over records with a cursor in SQL Server. It's lean but don't expect it to break performance records:

DECLARE @Value INT;
DECLARE cur CURSOR FOR SELECT Column FROM Table;
OPEN cur;

FETCH NEXT FROM cur INTO @Value;
WHILE @@FETCH_STATUS = 0 BEGIN
    -- Take a stroll through each record, printing @Value 
    FETCH NEXT FROM cur INTO @Value;
END;

CLOSE cur; DEALLOCATE cur;

Just misclick Ctrl+F and replace @Value, Column, and Table. Cursors are your pal for row-by-row chase but might turn into a snail race for voluminous datasets.

Selecting an efficient looping technique

Cursor versus while loop

When looping through records, cursor is the first friend that comes to mind. But have you ever tried inviting while loop to the party? It's a great buddy with temporary tables and pretty good at reducing the performance burden.

Temp tables need some love too

In the world of temporary tables, indexes are the glossy shine of an efficient data model. A well-indexed table is like a sprint runner on steroids—always gets you to the finish line faster.

Set-based operations are your friend

As much as we adore row-by-row processing, it's always fair to ask: Can this be a set-based operation? SQL Server handles set operations like a champ—it could be your saving grace from pesky loops.

Efficient resource management

Like cleaning up after a great dinner, deleting processed records keeps your temporary tables lean. It's also critical to drop the table and deallocate cursors once you're done—they aren't collector's items!

Loop mechanics and performance measures

Handling cursors like a pro

Cursors, while helpful, must be operated with care. Always validate the fetch status with @@FETCH_STATUS. If bound by cursors, strategically fetch top records for processing (like StatusID = 7 records—to infinity and beyond!).

Temporary table tactics

Maintaining a smooth SQL ride could involve identity columns, counters for iterations, and formatting data with CONVERT. Now, that's one well-oiled machinery you got there!