SQLite index performance - performance

Question

I have a table in the following layout
email, item_id, json where
email is a string
item_id is a unix timestamp in ms
json is the item data to be used with the JSON1 extension
and I also have a multi-column index on that table with email, id
I perform a lot of queries in the style of WHERE email = 'asd' AND item_id > ... AND item_id < ...
I've been dealing with MongoDB for too many years now, so I'm used to not dealing with database normalization, and just went with the easiest SQL table layout.
On a phone, a query for the abovementioned style can take up to a second for a 35000 item query. The index does get used.
Will I get a noticeable performance boost when I normalize the database by creating a new table with email, email_id and change the original to email_id, item_id, json and start querying via JOINS? In that case email, email_id would contain about 2-5 items and email_id, item_id, json many thousands.

Answer 1

Using 3 tests the original, a query using a JOIN and an additional option, using a subquery rather than a join to get the email id based upon the email address and compare this to the email_id. The subquery came out on top, the original fared worst.
Results were :-
SELECT * FROM original WHERE email = 'email3#ouremail.com' AND item_id > 7800 AND item_id < 2404327029516376406
OK
Time: 0.199s
SELECT * FROM item WHERE email_id = (SELECT email.email_id FROM email WHERE email.email = 'email3#ouremail.com') AND item_id > 7800 AND item_id < 2404327029516376406
OK
Time: 0.082s
SELECT * FROM item JOIN email ON item.email_id = email.email_id WHERE email.email = 'email3#ouremail.com' AND item_id > 7800 AND item_id < 2404327029516376406
OK
Time: 0.109s
The following was used to create and test :-
DROP TABLE IF EXISTS original;
CREATE TABLE IF NOT EXISTS original (email TEXT, item_id INTEGER, json BLOB, PRIMARY KEY(email,item_id));
WITH RECURSIVE cnt(x,y,z)
AS (
SELECT 'email'||(1 + ABS(random() / (9223372036854775807 / 5)))||'#ouremail.com',
ABS(random()),
randomblob(ABS(random() / (9223372036854775807 / 40) ))
UNION ALL SELECT
'email'||(1 + ABS(random() / (9223372036854775807 / 5)))||'#ouremail.com',
ABS(random()),
randomblob(ABS(random() / (9223372036854775807 / 40)))
FROM cnt LIMIT 350000
)
INSERT INTO original SELECT * FROM cnt;
DROP TABLE IF EXISTS email;
CREATE TABLE IF NOT EXISTS email (email_id INTEGER PRIMARY KEY, email TEXT);
INSERT INTO email SELECT DISTINCT null,email FROM original;
DROP TABLE IF EXISTS item;
CREATE TABLE IF NOT EXISTS item (email_id, item_id, json);
INSERT INTO item SELECT
(SELECT email_id FROM email WHERE original.email = email.email),
item_id,
json FROM original;
SELECT * FROM original WHERE email = 'email3#ouremail.com' AND item_id > 7800 AND item_id < 2404327029516376406;
SELECT * FROM item WHERE email_id = (SELECT email.email_id FROM email WHERE email.email = 'email3#ouremail.com') AND item_id > 7800 AND item_id < 2404327029516376406;
SELECT * FROM item JOIN email ON item.email_id = email.email_id WHERE email.email = 'email3#ouremail.com' AND item_id > 7800 AND item_id < 2404327029516376406;
You could worse then to run the following and look at the output.
EXPLAIN QUERY PLAN SELECT * FROM original WHERE email = 'email3#ouremail.com' AND item_id > 7800 AND item_id < 2404327029516376406;
EXPLAIN QUERY PLAN SELECT * FROM item WHERE email_id = (SELECT email.email_id FROM email WHERE email.email = 'email3#ouremail.com') AND item_id > 7800 AND item_id < 2404327029516376406;
EXPLAIN QUERY PLAN SELECT * FROM item JOIN email ON item.email_id = email.email_id WHERE email.email = 'email3#ouremail.com' AND item_id > 7800 AND item_id < 2404327029516376406;