How can I insert into Table3 the intersection of Table1 and Table2, except the entries that already exist in Table3?

Question

First, to find the intersection of Table1 and Table2 I have

SELECT Id FROM Table1
INTERSECT
SELECT Id FROM Table2

or

SELECT Table1.Id
    FROM Table1
    INNER JOIN Table2 ON Table1.Id=Table2.Id

Now I want to insert that into table3:

INSERT INTO Table3
SELECT Table1.Id
    FROM Table1
    INNER JOIN Table2 ON Table1.Id=Table2.Id

But the problem is that some Id I am trying to insert can be already in Table3 (and Id is the primary key, so it must be unique).

I have read https://stackoverflow.com/a/5288322/1529630 . Then, I have renamed Id to Id_ in Table3 to avoid conficts so that I can do

SELECT DISTINCT Id
FROM Table1 cr LEFT JOIN Table3 c ON cr.Id = c.Id_
WHERE c.Id_ IS NULL

But when I try to intersect...

SELECT Id FROM Table2

INTERSECT

SELECT DISTINCT Id
FROM Queue cr LEFT JOIN Excluded c ON cr.Id = c.Id_
WHERE c.Id_ IS NULL

...I get an error. What I am doing wrong? Is there a better way to do it?

Answer 1

If the problem is uniqueness of ids, try something like this:

INSERT INTO Table3(id)
    SELECT Table1.Id
    FROM Table1 INNER JOIN
         Table2
         ON Table1.Id=Table2.Id
    where Table1.Id not in (select Id from Table3);

EDIT:

I proposed the above because it seems the clearest way of expressing what you want. The equivalent using left outer join might perform better:

INSERT INTO Table3(id)
    SELECT Table1.Id
    FROM Table1 INNER JOIN
         Table2
         ON Table1.Id=Table2.Id left outer join
         Table3
         on Table1.id = Table3.id
    where Table3.id is null

You can also use INSERT OR IGNORE to ignore the error:

INSERT OR IGNORE INTO Table3(id)
    SELECT Table1.Id
    FROM Table1 INNER JOIN
         Table2
         ON Table1.Id=Table2.Id;