CODEWITHSUNDEEP
sqldatabaseindexing
vernal123
vernal123

Reputation: 129

SQL Indexing not improving speed

Given an SQL database with index for (startpage, endpage), with a relation Articles(*ID*, title, startpage, endpage), why isn't a query

SELECT title 
FROM Articles 
WHERE endpage = 100;

sped up by the previous index?

Apologies for this peculiar question as it came from a practice paper without explanation.

Upvotes: 0

Views: 334

Answers (1)

Bill Karwin
Bill Karwin

Reputation: 562260

Why the index shown does not help that query: because endpage is not the leftmost column of the index.

See my answer to Does Order of Fields of Multi-Column Index in MySQL Matter for more explanation (that question is about MySQL, but the answer should apply to any implementation of B-tree indexes).

Upvotes: 3

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