Room update based on selection - sql-update

Question

I am using Room in my application, and I wish to update the results based on a selection with order by.
The goal is to update the five top scoring results.
Inside my Dao class I have this query:
// Setting new five words
#Query("with data as( SELECT score FROM words_table ORDER BY score DESC LIMIT 5 )" +
" UPDATE data SET isInTodayWords= 1")
LiveData<List<Word>> setNewWords();
I get an error from the update statement - "can't resolve symbol data".
What am I missing in here?

Answer 1

I believe the issue is that you need to UPDATE the actual table not the CTE. Try :-
#Query("with data as( SELECT score FROM words_table ORDER BY score DESC LIMIT 5 )" +
" UPDATE words_table SET isInTodayWords= 1")
LiveData<List<Word>> setNewWords();
As per (qualified-table-name):-
Saying that I believe that you need to the utilise the CTA (data) in the WHERE clause otherwise all rows will be updated.
As such you likely want to add WHERE score IN data (see note below as this could apply, if a row has a unique column then you may prefer to extract that rather than the score and use it in the WHERE clause):-
#Query("WITH data AS (SELECT score FROM words_table ORDER BY score DESC LIMIT 5) UPDATE words_table SET isInTodaysWords = 1 WHERE score IN data")
An alternative approach could be to use :-
#Query("UPDATE words_table SET isInTodaysWords = 1 WHERE score >= (SELECT min(score) FROM (SELECT * FROM words_table ORDER BY score DESC LIMIT 5))")
However, if there were say 10 rows all with the same topscore then all 10 rows would be flagged.
If there was a unique column named _id then the following would restrict the flagging to the 5 selected rows :-
#Query("WITH data AS (SELECT _id FROM words_table ORDER BY score DESC LIMIT 5) UPDATE words_table SET isInTodaysWords = 1 WHERE _id IN data")