I'm trying to write a script that checks for multiple entries on a table in a 
database.  So far I've been
plagued by MySQL errors.  I'm fairly confident my scripting is ok (Then again, I've 
been wrong before.)  I think
moreover there might be some difficulty with my theory.  Then again, I could try and 
do this with MySQL join
statements.  Any feedback would be appreciated.
  Warning: Supplied argument is not a valid MySQL result resource in
/home/ufr2/underfoot-www/admin/dupeshows.html on line 51

I notice that others have addressed your PHP/interfacing issues...

You asked about "theory". The current solution will require n+1 calls to the database 
(where there are n-rows in
the local_shows table). That's quite 'expensive'.

Which is likely to be the 'best tool for the job' - an external scripting language 
(PHP) or the RDBMS itself

Consider a 'MySQL-oriented' solution:-

1 if the two fields (show_date and venue) were made into a UNIQUE index, then the 
check would become superfluous
because MySQL would ensure the situation never arose - at the cost of the time to 
perform the check/index
insertion at every row INSERT or UPDATE (although you may gain a speed increase for 
certain SELECTS)

2 performing the existing PHP routine using SQL - you show only a list of 'duplicates' 
(and no DELETE), so:

select show_date, venue, count(*) as freq
from local_shows
group by show_date, venue
having freq>1

will give you what you have attempted to code thus far.
(you may wish/need to juggle the sequence of show_date and venue to suit)


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