[sqlite] Functions and index

[hilaner]

I have hundred thousands of records in this table:

CREATE TABLE days (
        day_id INTEGER NOT NULL PRIMARY KEY,
        day_date DATE
);

CREATE INDEX day_i ON days (day_date ASC);

And then if I run such query:

EXPLAIN QUERY PLAN
SELECT JULIANDAY(MAX(day_date)) FROM days;
0|0|0|SCAN TABLE days (~1000000 rows)

it will do full table scan instead of use an index.

But:

EXPLAIN QUERY PLAN
SELECT MAX(day_date) FROM days;
0|0|0|SEARCH TABLE days USING COVERING INDEX day_i (~1 rows)

so it is as I expected.

Is there any other way to rewrite such kind of queries with functions?
The query below uses an index but it is much longer:

EXPLAIN QUERY PLAN
SELECT JULIANDAY(day_date) FROM days
   WHERE day_date IN (SELECT MAX(day_date) FROM days);
0|0|0|SEARCH TABLE days USING COVERING INDEX day_i (day_date=?) (~250 rows)
0|0|0|EXECUTE LIST SUBQUERY 1
1|0|0|SEARCH TABLE days USING COVERING INDEX day_i (~1 rows)

Best regards,
Adam
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