"*Question: Find the item_ids that are either 'INK-RESIN' or 'INK-WRSOL' but not both in the po_items table. Hint you need to use UNION and INTERSECT operations.*" If you see the dataset from items table as below, IRN and IWS have one entry each for 'INK-RESIN' and 'INK-WRSOL'. Hence none of these item_ids are having both description or multiple entries in items table. item_id|descr|on_hand|price P9|9KG PAPER|300|25.25 P12|12KG PAPER|700|49.99 P18|18KG PAPER|100|100 IRN|INK-RESIN|3|500 IWS|INK-WRSOL|5|350 CBD|CARDBOARD|47|15 Now po_items table has these item_ids. As per question, we should be getting 'IRN' and 'IWS' both but only 'IWS' is expected in the output. Is my understanding correct about this question?

Based on the limited data provided, we would get the output "IWS." For this question, we need to select the item_ids that are either IRN (associated with 'INK-RESIN') or IWS (associated with 'INK-WRSOL'), and then remove(we should use another operation here) any item_id that would appear with both descriptions ('INK-RESIN' and 'INK-WRSOL') by using UNION and INTERSECT.

I have the same question and you answer is a little bit confusing since based on the given data, each item id (IRN or IWS) appear with only one description for each (shown in the attached image) in the items table. Therefore, my understanding of question based on the given data suggest that the expected output in this case should be both IRN and IWS. Please correct me if there is anything wrong. Thank you!

yeah, I know what you mean. Our expected output based on the given data should be both IRN and IWS. But when we're intersecting the results of two queries,there are no common item_ids between these two, this part of the query is returning nothing,as a result, only IWS is being returned. You can have a try in your terminal. I think this issue with only getting IWS is likely due to the logic of EXCEPT and INTERSECT filtering out more than necessary.

I think it's the problem with the question. Even if the result returned by except is nothing, that is, it is equivalent to performing a union operation on IRN and IWS, it will also return two results. This is very simple logic.

It seems like sqlite doesn't allow parenthesis for select statement when performing UNION/EXCEPT/INTERSECT operators? Without parenthesis, after UNION we get IRN and IWS, next it will perform EXCEPT and the result will be IWS, lastly it will do INTERSECT so the final results it returns is IWS.

Yes it does appear to be an issue with the parenthesis, I tried adding them into the correct solution on the test interface and it does appear to break it, I'll investigate if this is an SQLite issue, or to do with the testing code implemented on the question itself. So for now don't use parenthesis for this one. Adam. "Yufang Wei" <24*1*1*3@s*u*e*t*u*a*e*u*a*> wrote:

I altered the question to give an error message referencing the unnecessary parenthesis as the reason for the error. It does appear SQLite doesn't like the use of them in SET statements and will raise an exception. Adam.