Update referencing on subquery (sqlite)

Question

I have a table with md5 sums for files and use the following query to find the files which exist in one hashing-run and not in the other (oldt vs newt):

SELECT *
FROM md5_sums as oldt
WHERE NOT EXISTS (SELECT *
                  FROM md5_sums as newt
                  WHERE oldt.file = newt.file
                  and oldt.relpath = newt.relpath
                  and newt.starttime = 234)
and oldt.starttime = 123

now i want to put a flag in an extra column with an update clause, like

update md5_sums
set only_in_old = 'X'
where

and there i want a reference to the upper query as subquery, but i cannot find a proper way. Is there a possibility to use the results from the upper query for the where clause from the update-query? (I added now some Table Screenshots with simple Table Data)

Table Description

Table Data before UPDATE

desired Table Data after UPDATE

Answer 1

SQLite does not support aliasing the updated table.
In your case you don't need that.
You can use the table's name md5_sums inside the subquery since you aliased the table of the SELECT statement as newt .

UPDATE md5_sums 
SET only_in_old = 'X'
WHERE NOT EXISTS (
  SELECT 1 FROM md5_sums AS newt
  WHERE md5_sums.file = newt.file
  AND md5_sums.relpath = newt.relpath
  AND newt.starttime = 234
)
AND starttime = 123

See the demo .
Results:

| file    | relpath  | starttime | only_in_old |
| ------- | -------- | --------- | ----------- |
| abc.txt | /var/tmp | 123       |             |
| abc.txt | /var/tmp | 234       |             |
| def.txt | /tmp     | 123       | X           |
| xyz.txt | /tmp     | 234       |             |

Answer 2

I hope this helps you in converting the select statement into an update statement,

UPDATE md5_sums 
SET only_in_old = 'X'

WHERE NOT EXISTS (SELECT *
                  FROM md5_sums newt
                  WHERE file = newt.file
                  and relpath = newt.relpath
                  and newt.starttime = 1551085649.7764235)
and starttime = 1551085580.009046