# 3.2.1 The Scouts (Scans)  Before any matchmaking or organizing can happen, someone has to actually go out into the mud and retrieve the shipping containers. In the Query Algebra, this is the job of the **Scouts**, officially known as **Scan Nodes**. The Scouts are the only soldiers in the entire army who actually touch the heavy metal shelves of the disk. ## Sequential Scan: The Brute Force Company The **[[Operations/SeqScan|Sequential Scan]]** is the most honest, yet most exhausting way to find a suitcase. Imagine a tired elephant walking down every single aisle of the warehouse, opening every single physical container, and checking every single suitcase inside. If the Admiral asks, "Find me all suitcases containing blue socks," the Sequential Scan will check *all ten million suitcases* just to be absolutely sure none were missed. It is the path of maximum resistance. ## Index Scan: The Scouts on Stilts The **[[Operations/IndexScan|Index Scan]]** avoids the mud entirely. These specialized scouts use the **[[Chapter 2/2.1 - The B-Tree|Index Clerk's Map]]** to pinpoint the exact GPS coordinates of a required suitcase. They walk directly to a specific container, grab the one suitcase, and vanish. "Snipers," the elephant nods respectfully. ## Bitmap Heap Scan: The Whiteboard Team What if the Admiral needs five thousand scattered suitcases? Walking back and forth between the Index Clerk and the warehouse five thousand times would cause absolute chaos. Enter the **[[Operations/BitmapHeapScan|Bitmap Heap Scan]]**. First, they scan the Index and mark every required container location on a giant whiteboard (the Bitmap Index Scan). Then, they organize a route to visit each container *exactly once*, collecting all necessary suitcases from a container before moving to the next. Pure, lazy efficiency! --- [[Chapter 3/3.2 - Query Algebra|← 3.2 - Query Algebra]] | [[Chapter 3/3.2 - Query Algebra|↑ 3.2 - Query Algebra]] | [[Chapter 3/3.2.2 - The Matchmakers (Joins)|3.2.2 - The Matchmakers (Joins) →]]