SQLite Forum

Feature request: extensions to UPDATE
UPDATE is already implemented as a SELECT of ROWID, unchanged fields and SET fields followed by an INSERT of the new row 

UPDATE a SET bunny=1 WHERE EXISTS (SELECT 1 FROM b WHERE a.this = b.that);

asql> explain query plan update a set bunny=1 where exists (select 1 from b where a.this = b.that);
id    parent         notu  deta
----  -------------  ----  ----
4     0              0     SCAN TABLE a
6     0              0     CORRELATED SCALAR SUBQUERY
10    6              0     SEARCH TABLE b USING COVERING INDEX b_that (that=?)