How to UPDATE in SQLite using a LEFT JOIN to select candidate rows

I have a table assoc containing columns

local_id,开发者_高级运维 remote_id, cachedData

I can successfully run an SQLITE query that looks like

SELECT a1.local_id, a1.remote_id FROM assoc a1 LEFT JOIN ....

so that I identify certain rows of the assoc table that meet my criteria.

What I would like to do is to set cachedData to null in those rows.

How can I do this? Sqlite doesn't support UPDATE with joins; you can issue subqueries but I can't figure out how to get the syntax correct; it seems nonintuitive to me.

---

 UPDATE assoc SET cachedData = NULL
    WHERE EXISTS (SELECT * FROM otherTable 
        WHERE otherTable.Col1 = assoc.Col1 AND otherTable.Col2 = assoc.Col1)

Be aware that this is not especially performant.

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If assoc has a single column as the primary key (and assuming that it is local_id):

UPDATE assoc
SET cachedData=NULL
WHERE local_id IN (
  SELECT local_id FROM assoc a1 LEFT JOIN ...
);

---

Aha, there's already a builtin rowid!

UPDATE assoc
SET cachedData=NULL
WHERE rowid IN (
   SELECT rowid FROM assoc a1 LEFT JOIN ...
);