Is it possible to perform a SELECT and an UPDATE in a single SQLite query? - sqlite

Question

I might not be wording the title properly but I'm wondering if it's possible to both read data and update data in a single query (or multiple queries in a single call?) using SQLite.
As an example situation I would like to SELECT the current state of the database then UPDATE the state to something new all in one single atomic query.
Here is how I'm pulling this off using Postgres:
UPDATE migrations_lock
SET is_locked = 0
WHERE index = 1 RETURNING (
SELECT is_locked AS was_locked
FROM migrations_lock
WHERE index = 1
);
Likewise, I'm able to achieve the same thing in MySQL using a transaction:
START TRANSACTION;
SELECT is_locked AS was_locked
FROM migrations_lock
WHERE `index` = 1;
UPDATE migrations_lock
SET is_locked = 0
WHERE `index` = 1;
COMMIT;
Sadly, running the same Postgres query in SQLite returns the new data instead of the existing data. Running the equivalent MySQL query in SQLite form (BEGIN TRANSACTION) returns an error about nested transactions. Running the SELECT followed by the UPDATE query in a single call (without the transaction) results in the SELECT query running and the UPDATE query being ignored.
There is some additional context about how the query is being run in this pull request.

Answer 1

SQLite since version 3.33.0 supports UPDATE FROM see
https://www.sqlite.org/lang_update.html#update_from
Another possibility is to use a CTE (Common Table Expression) to drive an UPDATE as per
All common table expressions (ordinary and recursive) are created by prepending a WITH clause in front of a SELECT, INSERT, DELETE, or UPDATE statement. A single WITH clause can specify one or more common table expressions, some of which are ordinary and some of which are recursive.
https://www.sqlite.org/lang_with.html
An example of using a CTE to drive an update:-
DROP TABLE IF EXISTS test;
CREATE TABLE IF NOT EXISTS test (datee TEXT, other_colmumns);
INSERT INTO test VALUES ('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
,('not the date I wanted','otherdate')
;
SELECT rowid,* FROM test; /* result 1 prior to update */
/* The CTE driven UPDATE */
WITH x AS (SELECT rowid FROM test LIMIT 10,5)
UPDATE test SET datee = '19/12/2021' WHERE test.rowid IN (SELECT * FROM x)
;
SELECT rowid,* FROM test; /* result 2 after update */
DROP TABLE IF EXISTS test; /* clean up */
Result 1 being
Result 2 being
Modifying the CTE for multiple selects (2 ctes x and y):-
/* The CTE driven UPDATE */
WITH x AS (SELECT rowid FROM test LIMIT 10,5),
y as (SELECT rowid FROM test LIMIT 1,2)
UPDATE test SET datee = '19/12/2021' WHERE test.rowid IN (SELECT * FROM x UNION ALL SELECT * FROM y)
;
result 2 is then