SQLite

The SQLite Bytecode Engine (has opcode references)
SQL references

See tables and indices:

SELECT name FROM sqlite_master
WHERE type='table';

SELECT name FROM sqlite_master
WHERE type='index';

Index

-- Single index
-- Table: books field: author_id
CREATE INDEX index_books_on_author_id on books(author_id);
DROP INDEX index_books_on_author_id;

-- Compound index
-- Table: books_readers fields: user_id, book_id
CREATE INDEX index_books_readers_on_user_id_and_book_id on books_readers(user_id, book_id);
DROP INDEX index_books_readers_on_user_id_and_book_id;

Explain

Explain syntax

EXPLAIN SELECT
EXPLAIN QUERY PLAN SELECT

Explain Query Plan

SCAN TABLE = Full Table Scan
SEARCH TABLE = Search part of Table by some indexes