Example INTERSECT queries

Compare the following example with the first UNION example. The only difference between the two examples is the set operator that is used, but the results are very different. Only one of the rows is the same:

235494 |    23875 |    8771

This is the only row in the limited result of 5 rows that was found in both tables.

select listid, sellerid, eventid from listing
intersect
select listid, sellerid, eventid from sales

listid | sellerid | eventid
--------+----------+---------
235494 |    23875 |    8771
235482 |     1067 |    2667
235479 |     1589 |    7303
235476 |    15550 |     793
235475 |    22306 |    7848

The following query finds events (for which tickets were sold) that occurred at venues in both New York City and Los Angeles in March. The difference between the two query expressions is the constraint on the VENUECITY column.

select distinct eventname from event, sales, venue
where event.eventid=sales.eventid and event.venueid=venue.venueid
and date_part(month,starttime)=3 and venuecity='Los Angeles'
intersect
select distinct eventname from event, sales, venue
where event.eventid=sales.eventid and event.venueid=venue.venueid
and date_part(month,starttime)=3 and venuecity='New York City';

eventname
----------------------------
A Streetcar Named Desire
Dirty Dancing
Electra
Running with Annalise
Hairspray
Mary Poppins
November
Oliver!
Return To Forever
Rhinoceros
South Pacific
The 39 Steps
The Bacchae
The Caucasian Chalk Circle
The Country Girl
Wicked
Woyzeck