Query using automatic index (log warning)

SQLITE_WARNING_AUTOINDEX (284) is passed to the sqlite3_log() callback when the query planner creates an automatic index to satisfy a join or WHERE clause. It is a performance warning, not an error.

1. 1JOIN or WHERE clause on a column with no index.
2. 2Subquery result used as a join source without an index.

Query execution when the planner decides to create a transient automatic index.

-- Trigger automatic index:
CREATE TABLE a(x); CREATE TABLE b(x);
INSERT INTO a VALUES(1),(2),(3);
INSERT INTO b VALUES(2),(3),(4);
-- No index on b.x:
SELECT * FROM a JOIN b ON a.x = b.x;
-- Log: "automatic index on b(x)"

Log warning: "automatic index on b(x)"

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