SQLite AUTOINCREMENT non-primary key column - sqlite

Question

I have the following SQLite table:
CREATE TABLE podcast_search (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
search TEXT NOT NULL UNIQUE
)
Whenever a user inserts/updates a row in the table, I want to sort that row at the end of the table. Thus, if I insert the following values:
_id | search | sort
===================
1 | foo | 1
2 | bar | 2
3 | quiz | 3
And then later update the 1 row from foo to foo2, the values should look like:
_id | search | sort
===================
2 | bar | 2
3 | quiz | 3
1 | foo2 | 4
I've implemented this thusly:
CREATE TABLE podcast_search (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
search TEXT NOT NULL UNIQUE,
update_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
)
CREATE TRIGGER update_date_update_trigger
AFTER UPDATE ON podcast_search FOR EACH ROW
BEGIN
UPDATE podcast_search
SET update_date = CURRENT_TIMESTAMP
WHERE _id = OLD._id;
END
However, my unit tests require a 1000ms sleep between insert/update operations in order to reliably sort, and this amount of delay is very annoying for unit testing.
I thought I could implement a vector clock instead, but it seems that AUTOINCREMENT values only exist for primary key columns. Does SQLite offer any other AUTOINCREMENT or AUTOINCREMENT-like option?
I'm running this on Android P, but this should be a generic SQLite problem.
UPDATE
I'm now using an sort INTEGER NOT NULL UNIQUE column, and SELECT-ing the largest row in that column and manually incrementing it before an INSERT/UPDATE:
CREATE TABLE podcast_search (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
search TEXT NOT NULL UNIQUE,
sort INTEGER NOT NULL UNIQUE
)
SELECT sort from podcast_search ORDER BY sort DESC
either increment sort in application code, or set it to 0
Could I do this in a TRIGGER instead?

Answer 1

I thought I could implement a vector clock instead, but it seems that
AUTOINCREMENT values only exist for primary key columns. Does SQLite
offer any other AUTOINCREMENT or AUTOINCREMENT-like option?
They are not in fact AUTOINCREMENT values rather a column with AUTOINCREMENT will be an alias of the rowid column; not because AUTOINCREMENT has been coded but because INTEGER PRIMARY KEY has been coded.
All coding AUTOINCREMENT does is add a constraint that an auto-generated value MUST be greater than any other existing or used value. This only in fact becomes apparent if when a rowid with the value of 9223372036854775807 exists. In which case an attempt to insert a new row with an auto-generated rowid (i.e. no value is specified for the rowid column or an alias thereof) will result in an SQLITE_FULL error.
Without AUTOINCREMENT and when the highest rowid is 9223372036854775807 (the highest possible value for a rowid) an attempt is made to use a free value, which would obviously be lower than 9223372036854775807.
SQLite Autoincrement
You may wish to note the very first line of the linked page which says :-
The AUTOINCREMENT keyword imposes extra CPU, memory, disk space, and
disk I/O overhead and should be avoided if not strictly needed. It is
usually not needed.
I can't see any need from your description.
So what you want is a means of assigning a value for the column that is to be sorted that is 1 greater than the highest current value for that column, so it becomes the latest for sorting purposes, a subquery that retrieves max(the_column) + 1 would do what you wish. This could be in an UPDATE, TRIGGER or in an INSERT.
rowid = max(rowid) + 1 is basically how SQLite assigns a value to rowid unless AUTOINCREMENT is used when 1 is added to the greater of max(rowid) and the value, for the respective table, obtained from the table sqlite_sequence (will only exist if AUTOINCREMENT is used). It is referencing and maintaining sqlite_sequence that incurs the penalties.
For example you could use the following (which eliminates the need for an additional column and the additional index) :-
-- SETUP THE DATA FOR TESTING
DROP TABLE IF EXISTS podcast_searchv1;
CREATE TABLE IF NOT EXISTS podcast_searchv1 (
_id INTEGER NOT NULL PRIMARY KEY,
search TEXT NOT NULL UNIQUE
);
INSERT INTO podcast_searchv1 (search)
VALUES('foo'),('bar'),('guide')
;
-- Show original data
SELECT * FROM podcast_searchv1;
-- DO THE UPDATE
UPDATE podcast_searchv1 SET search = 'new value', _id = (SELECT max(_id) + 1 FROM podcast_searchv1) WHERE search = 'foo';
-- Show the changed data
SELECT * FROM podcast_searchv1;
The results being :-
and then :-