That's the equivalent of limitby(0,2). See the example in the book:
http://web2py.com/books/default/chapter/29/06/the-database-abstraction-layer#orderby--groupby--limitby--distinct--having-orderby_on_limitby-left-cache
Yes, the example I gave you was crude, and a bit incorrect - the limitby
takes in two offsets: min and max. Look up the documentation. Also, you
need to ensure that if you want the last two entries, that atleast two
entries exist, and so on. Also, it is not very efficient if you are
frequently going to call a "count" on the database. Lookup some of the
performance tricks for this, particular to your database.
________________________________________
Kiran Subbaraman
http://subbaraman.wordpress.com/about/
On Thu, 08-01-2015 5:14 PM, Timo Bahner wrote:
Thanks, it works with
|
total_entries =db(db.test.id >0).count()
[next_to_last,last]=db().select(db.test.ALL,limitby=(total_entries-3,2))
|
But crashes with more than 3 entries:
|
ValueError: need more than1 value to unpack
|
However, it works this way (switched "3" with "total_entries"):
|
[next_to_last,last]=db().select(db.kpi.ALL,limitby=(total_entries-*total_entries*,2))
|
Question: Could this cause a problem (math or otherwise)?
On Thursday, January 8, 2015 6:55:28 AM UTC+1, Kiran Subbaraman wrote:
Am assuming you want the last two records in a table all the time,
and they correspond to the variables A, B.
If you know the number of records in that table, via the count
method, or a more efficient mechanism, then you can use the
limitby statement to get the last two records.
|
total_records = #number of records in the test table - computed
via count, or some other method
[A,B] =db().select(db.test.ALL, limitby(total_records - 3, 2)
|
________________________________________
Kiran Subbaraman
http://subbaraman.wordpress.com/about/
<http://subbaraman.wordpress.com/about/>
On Thu, 08-01-2015 10:56 AM, Timo Bahner wrote:
Hi guys.
Let's assume the following table
|
db.define_table('test',Field('letter','double'))
|
How can I compare two 'letter' entries if for example
|
A=1.23
B=4.56
|
To get the last entry (B) I'll use
|
last_entry =db().select(db.test.ALL).last()
|
*But how do I get the entry before the last, in this case letter
A?* The actual comparing will be done within index.html to check
if B is greater or equal to A for example
|
{{ifB >=A:}}
<!--some html code-->
{{else:}}
<!--some html code-->
{{pass}}
|
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