Hello All, There have been a few items on this subject on the list recently and I now have cause to do a query of this kind myself. I'm trying to identify which items that occur in one table that do not occur in another. Both tables have a unique ID field. I know the standard procedure is as follows: - Select * From Table1 Where ID Not In(Select ID From Table2) Whenever I've used this query with large data sets (16,000 records) it takes ages to perform - more than 30 minutes. There is also nothing to indicate that MapInfo is actually doing anything. Being somewhat impatient, I hit the ESC key after about 1 minute and tried another method as follows. Use the Update Table function to add a temporary column to Table1. Compute the join using Table1.ID = Table2.ID and calculate the value of the temporary column with the value of Table2.ID. This works almost instantaneously and allows me to identify the items that are not in Table2 by selecting the rows in a table1 with a null value in the new temporary column. I'd like a confirmation that my second method is correct, and assuming it is, why does the first method take so long in comparison? Any comments are much appreciated. Keith ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
