Re: nested select statement syntax error

[Roland Bouman]

Easy!

SELECT orderno
FROM orders o
LEFT JOIN temporder t
ON o.orderno = t.orderno
WHERE t.orderno IS NULL

Like the INNER JOIN operator, the LEFT JOIN operator combines all records from the two table operands and retains those combinations for which the ON condition is true.
The difference is, that if the record from 'left' table (the table appearing left of the INNER JOIN operator) does not match any of the records in the right table (the table appearing right the INNER JOIN operator) it retains the left record, and makes up a virtual record for the right table composed out of NULLs. So, it's "match if you can, but don't lose the record if you can't".
Now, by adding the WHERE t.orderno IS NULL, we are effectively filtering out all the records that matched, retaining those that can't match.

Good luck!