问题
I need to delete rows from an SQLite table where their row IDs do not exist in another table. The SELECT statement returns the correct rows:
SELECT * FROM cache LEFT JOIN main ON cache.id=main.id WHERE main.id IS NULL;
However, the delete statement generates an error from SQLIte:
DELETE FROM cache LEFT JOIN main ON cache.id=main.id WHERE main.id IS NULL;
The error is: SQLite Error 1 - near "left": syntax error. Is there another syntax I could use?
回答1:
SQLite apparently doesn't support joins with the delete statement, as you can see on the Syntax diagrams. You should however be able to use a subquery to delete them.
ie.
DELETE FROM cache WHERE id IN
(SELECT cache.id FROM cache LEFT JOIN main ON cache.id=main.id WHERE main.id IS NULL);
(Not tested)
回答2:
Since you going down the route of subquery, might as well get rid of the join altogether and simplify the query:
DELETE FROM cache WHERE id NOT IN (SELECT id from main);
来源：https://stackoverflow.com/questions/4967135/deleting-rows-from-sqlite-table-when-no-match-exists-in-another-table