IndexesWhat an index does, when it helps, and what it costs.ComputingA separate sorted structure — usually a B-tree — that lets thedatabase find rows without scanning the table. It trades writespeed and disk space for read speed.STRUCTUREB-treeREADfasterWRITEslowerIndex columns used in WHERE, JOIN and ORDER BY.A composite index works left to right: (a, b) helps queries on a, and on a+b, but not b alone.Wrapping a column in a function usually disables its index.Every index must be updated on every insert, update and delete.A low-cardinality column — like a boolean — rarely benefits.EXPLAIN shows whether the index was actually used.LOOK FOR ITWHERE lower(email) = 'x' cannot use an index on email. An index onlower(email) can.Always check with EXPLAIN. An index that is never chosen by theplanner is pure cost.Indexeslearnposters.com
Indexes — printable computing wall chart from LearnPosters. Free vector PDF, US Letter and A4.

What’s on the Indexes poster

A definition and 6 facts worth remembering.

A separate sorted structure — usually a B-tree — that lets the database find rows without scanning the table. It trades write speed and disk space for read speed.

Always check with EXPLAIN. An index that is never chosen by the planner is pure cost.

Questions about the Indexes poster

What’s on the Indexes poster?
A definition and 6 facts worth remembering. A separate sorted structure — usually a B-tree — that lets the database find rows without scanning the table. It trades write speed and disk space for read speed. Index columns used in WHERE, JOIN and ORDER BY.; A composite index works left to right: (a, b) helps queries on a, and on a+b, but not…; Wrapping a column in a function usually disables its index.; Every index must be updated on every insert, update and delete.; A low-cardinality column — like a boolean — rarely benefits.; EXPLAIN shows whether the index was actually used.; Structure — B-tree; Read — faster; Write — slower; WHERE lower(email) = 'x' cannot use an index on email. An index on lower(email) can.. Always check with EXPLAIN. An index that is never chosen by the planner is pure cost.
Who is the Indexes poster for?
Indexes belongs to the Computing section rather than to a school year, because computing is not something one grade owns. Anyone learning data can pin it up — a beginner, a student mid-course, or someone revising years later.
When should you use the Indexes poster?
Index the columns you filter and join on. Every index makes writes slower. A wall chart earns its place by being glanceable from where the work is happening, so Indexes belongs on the wall where that computing work actually happens, within glancing distance, rather than filed away.
What other posters go with Indexes?
ACID, The CAP Theorem and Choosing a Chart sit alongside Indexes in the Computing section. Printed together they make a wall rather than a single sheet, which is how a reference set actually gets used.ACIDThe CAP TheoremChoosing a Chart
Is the Indexes poster free to download and print?
Yes. Indexes downloads as a free PDF with no account, no email and no watermark, like everything else in the Computing section. Print as many copies as you like for a home, a classroom, a library or a tutoring group; reselling the file is the only thing the licence rules out.Read the licence
What size does the Indexes poster print at?
Indexes is a vector PDF laid out for US Letter, and prints on A4 with Fit to page — the same file, no separate download. Because every mark on it is drawn rather than photographed, it stays sharp enlarged to A3, A2 or A1 at a copy shop. Colour carries emphasis only, so a greyscale print of Indexes loses nothing.Printing guide

Related posters

Charts that sit alongside Indexes on the same wall.

Browse every Computing poster, or start from the full catalogue.