How to speed up Update SQLite?

Question

SQLite

Have a request

UPDATE qTable SET n = (SELECT COUNT(sP) FROM sTable WHERE sTable.uID = 181206113231
 AND sP = qTable.id GROUP BY sP);

on 20 thousand rows, it runs for almost a minute, which is very long, despite the fact that the SELECT subquery

SELECT COUNT(sP) FROM sTable, qTable. WHERE sTable.uID = 181206113231
 AND sP = qTable.id GROUP BY sP

runs in 0.006 seconds
Tell me how to speed up Update?