How to check if sql query result is empty in web.py/python

Question

I'm working on a web application in the web.py framework and need a way for web.py/python to check if the result of a sql query is empty.

Here's my current function:

def get_hours(): result = dbconn.query("select * from hours where date < (select max(date) from last_export) order by date DESC") return result

This works as expected, but I want the function to return False if the result of the query is empty. I already know that python has no way of returning how many elements there is in a iterable object(which is returned by the dbconn.query no matter if it's empty or not), without a count for loop. Which to me wouldn't work since i don't want the result to be iterated BEFORE it's returned.

Here's an example of what I want to achieve with the function:

def get_hours(): result = dbconn.query("select * from hours where date < (select max(date) from last_export) order by date DESC") if <result is empty/no rows/nothing to iterate>: return False else: return result

Any suggestions?

Community · Accepted Answer · 2017-05-23 12:14:31Z

2

def get_hours(): result = dbconn.query("select * from hours where date < (select max(date) from last_export) order by date DESC") if result: return result else: return False

Here is very interesting answer for further details:

https://stackoverflow.com/a/2710949/492258

edited May 23, 2017 at 12:14

CommunityBot

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answered Jan 1, 2012 at 18:19

asdf_enel_hak

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2 Comments

simen Over a year ago

Thank you! Exactly what I was looking for. So how do I know what a certain function returns? Both dbconn.query("myquery") and the variable 'result' prints only <web.utils.IterBetter instance..> in the interpreter, with no indicate that it's true or false.

boyfromnorth Over a year ago

This won't work cause even if the query returns nothing it will still go the the if part in this case.So put a check before executing the query . Answered below

Community · Accepted Answer · 2017-05-23 11:52:06Z

Here's a related (duplicate?) question on testing whether a generator has any items, which contains several suggestions to work around this limitation. As far as I know, Python does not have a simple way of testing whether an iterator is empty.

boyfromnorth · Accepted Answer · 2013-10-29 11:59:56Z

Try this:

def get_hours(): check = False results = dbconn.query("select * from hours where date < (select max(date) from last_export) order by date DESC") for result in results: check = True #Do stuff here if check == False: return false #query returned nothing

Gino Mempin · Accepted Answer · 2020-08-12 00:31:02Z

For MySQL Python:

data = self.cur.fetchall() if len(data) == 0: self.statusbar.showMessage(" NoRecord her") else: print("avaiable recored")

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