Why does this delete query run forever?

[sumdumgai]

This delete query runs forever and I have to kill it.

DELETE * FROM Table1
WHERE Table 1.Field1 NOT IN (SELECT DISTINCT Field1 FROM Table 2 where Field1 is not null);

Table1 has about 5,000 records and Table2 has about 300,000 records.
If I first create Table3 of distinct Field1's and then do:

DELETE * FROM Table1
WHERE Field1 not in (Select Field1 From Table3);

it runs quickly. But I would rather not create the Table 3.
Thanks for any help.

 

[ByteMyzer]

Try this:

DELETE * FROM Table1
WHERE NOT EXISTS (
    SELECT Table2.Field1 FROM Table2
    WHERE Table2.Field1 = Table1.Field1);

 

[sumdumgai]

Blazingly fast! Thanks a heap.