Think in Sets: Writing High-Performance SQL the Declarative Way

Think in Sets: Writing High-Performance SQL the Declarative Way “SQL is not about loops—it's about logic. The sooner you let go of procedural thinking, the faster your queries fly.” If you’ve come from a programming background, chances are your instinct is to iterate. But SQL wasn’t designed for that. SQL speaks the language of sets, and when you think in sets, your queries become: Faster More readable Easier to maintain In this article, we’ll compare procedural vs set-based logic with clear examples and best practices. The Problem: Updating Order Statuses Scenario: Mark all Pending orders as Shipped. ❌ Procedural Style with Cursors (SQL Server) DECLARE order_cursor CURSOR FOR SELECT id FROM Orders WHERE status = 'Pending'; DECLARE @id INT; OPEN order_cursor; FETCH NEXT FROM order_cursor INTO @id; WHILE @@FETCH_STATUS = 0 BEGIN UPDATE Orders SET status = 'Shipped' WHERE id = @id; FETCH NEXT FROM order_cursor INTO @id; END CLOSE order_cursor; DEALLOCATE order_cursor;

May 12, 2025 - 22:04

Think in Sets: Writing High-Performance SQL the Declarative Way

“SQL is not about loops—it's about logic. The sooner you let go of procedural thinking, the faster your queries fly.”

If you’ve come from a programming background, chances are your instinct is to iterate. But SQL wasn’t designed for that. SQL speaks the language of sets, and when you think in sets, your queries become:

Faster
More readable
Easier to maintain

In this article, we’ll compare procedural vs set-based logic with clear examples and best practices.

The Problem: Updating Order Statuses

Scenario: Mark all Pending orders as Shipped.

❌ Procedural Style with Cursors (SQL Server)

DECLARE order_cursor CURSOR FOR
SELECT id FROM Orders WHERE status = 'Pending';

DECLARE @id INT;
OPEN order_cursor;
FETCH NEXT FROM order_cursor INTO @id;

WHILE @@FETCH_STATUS = 0
BEGIN
  UPDATE Orders SET status = 'Shipped' WHERE id = @id;
  FETCH NEXT FROM order_cursor INTO @id;
END

CLOSE order_cursor;
DEALLOCATE order_cursor;