SQLite how to limit the number of records - c++

Question

I want to limit the number of records in my SQLite table to for example 100 records, and then when I INSERT the 101th record, the first record (the oldest) be removed from the table. In other word, I want to prevent the table from growing more than 100 records and always have the last 100 records. Is there any setting or query with SQLite or should I handle it manually?
thanks in advance

Answer 1

You can do it with a trigger.
Say that your table is this:
CREATE TABLE tablename (
id INTEGER PRIMARY KEY,
name TEXT,
inserted_at TEXT DEFAULT (strftime('%Y-%m-%d %H:%M:%f', 'now'))
);
In the column inserted_at you will have the timestamp of the insertion of each row.
This is not necessary if you declared the column id as:
id INTEGER PRIMARY KEY AUTOINCREMENT
because in this case you could identify the 1st inserted row by the minimum value of the id.
Now create this trigger:
CREATE TRIGGER keep_100_rows AFTER INSERT ON tablename
WHEN (SELECT COUNT(*) FROM tablename) > 100
BEGIN
DELETE FROM tablename
WHERE id = (SELECT id FROM tablename ORDER BY inserted_at, id LIMIT 1);
-- or if you define id as AUTOINCREMENT
-- WHERE id = (SELECT MIN(id) FROM tablename);
END;
END;
Every time that you insert a new row, the trigger will check if the table has more than 100 rows and if it does it will delete the 1st inserted row.
See the demo (for max 3 rows).