It's a bit more subtle than that. Certain strings, [\xff]*, have no end_row. If you want all rows starting with '\xff\xff' say, you'd have to set that as a lower bound and have no upper bound. Here's some Python:
def prefixSuccessor(s):
if not s:
return None
elif s[-1] != '\xff':
return s[:-1] + chr(1+ord(s[-1]))
else:
return prefixSuccessor(s[:-1])
def test():
assert prefixSuccessor('') == None
assert prefixSuccessor('abc') == 'abd'
assert prefixSuccessor('123\xff\xff') == '124'
assert prefixSuccessor('\xff\xff\xff') == None
In the cases where the successor function returns None, you should have no
upper bound in your query.
On Thu, Jan 21, 2010 at 4:12 AM, Stanislav Yudin <[email protected]> wrote:
> Thanks Luke and Sanjit.
> That "magic" in Parser.h in case of python looks like:
> end_row_id = id[:len(start_row)-1] + chr(ord(start_row[len(start_row)-1:])
> + 1)
>
> So since we're going to use it, please try not to break start_row/end_row
> in RowInterval while refactoring.
>
>
> On Thu, Jan 21, 2010 at 5:03 AM, Sanjit Jhala <[email protected]> wrote:
>
>> Basically "bas" is the first string that sorts after everything that
>> starts with "bar". A simple way to generate it is add 1 to last non- 0xff
>> byte of the of the start row string.
>>
>> -Sanjit
>>
>>
>>
>> On Wed, Jan 20, 2010 at 10:20 AM, Stanislav Yudin <[email protected]>wrote:
>>
>>> Thanks Sanjit, but this is not a solution. I don't know what should be
>>> "bas" in my case, since all I have is a predicate for row key, so I have to
>>> supply something like "barXXXXXXXX..." as end row, which should be the last
>>> posible key with such predicate. What I am looking for is the same logic as
>>> in src/cc/HyperTable/Lib/HqlParser.h:783 onwards (which looks like black
>>> magic for me). Can you explain what is going on in HqlParser.h? I am using
>>> thrift bindings for python.
>>>
>>> On Wed, Jan 20, 2010 at 10:24 PM, Sanjit Jhala <[email protected]>wrote:
>>>
>>>> Hi Stanislav,
>>>>
>>>> Suppose you want to set up a scanner that returns all rows starting with
>>>> "bar". Setup a scanner with the row interval start_row = 'bar', end_row =
>>>> 'bas', start_inclusive = true, end_inclusive = false.
>>>>
>>>> Btw are you using the Thrift interface or the C++ client?
>>>>
>>>> -Sanjit
>>>>
>>>> On Wed, Jan 20, 2010 at 4:40 AM, Stanislav Yudin <[email protected]>wrote:
>>>>
>>>>> Hello everyone,
>>>>> I wonder what is the best way to setup ScanSpec which would do the same
>>>>> as =^ (or RELOP_SW) operator in HQL?
>>>>>
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