Question

Write a SQL query to find those values from column A in table X that are NOT present in column B of table Y.

update: the query is taking too long with not in(more than 5 minutes, i didn’t wait for it to complete) The column B in table Y is a primary key.

update: im using oracle. The table size is in millions(rows) for both tables. Of course, I’m using another WHERE clause, which means I’m comparing about 500,000 rows of table X with millions of rows in table Y

Answer 1

There are 4 ways to do this that I can think of.

• Not In (careful of NULLs)
• OUTER JOIN
  and filter on NULL (may need DISTINCT added)
• NOT EXISTS
• EXCEPT (Following update in question Oracle uses the non standard MINUS operator for this)

This last one appears to be the preferred way of doing it in Oracle though I can’t vouch for that myself.