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Database / SQLite Interview questions

Why might full-text search (FTS5) be needed instead of a LIKE query?

A LIKE '%word%' query has to scan every row and check the pattern against each one, since a leading wildcard prevents SQLite from using a normal B-tree index at all — on a large table, this means a full table scan for every search, which gets slower as the table grows and offers none of the relevance-ranking or linguistic features (stemming, tokenization) a real search feature typically needs.

-- slow: full table scan, no relevance ranking
SELECT * FROM articles WHERE body LIKE '%database%';

-- FTS5: indexed, ranked full-text search
CREATE VIRTUAL TABLE articles_fts USING fts5(title, body);
SELECT * FROM articles_fts WHERE articles_fts MATCH 'database';

FTS5 is SQLite's built-in full-text search extension: it builds a specialized inverted index over the text (mapping words to the rows containing them), supporting fast MATCH queries, relevance ranking, phrase search, and prefix matching — capabilities a plain LIKE scan simply can't provide efficiently or at all, regardless of table size.

Why can't a normal B-tree index help a `LIKE '%word%'` query?
What capability does FTS5 provide that plain LIKE cannot?

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