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From DuyHai Doan <doanduy...@gmail.com>
Subject Re: How to query '%' character using LIKE operator in Cassandra 3.7?
Date Mon, 26 Sep 2016 14:07:12 GMT
"In the current implementation (‘%’ could be a wildcard only at the
start/end of a term) I guess it should be ’ENDS with ‘%escape’ ‘."

--> Yes in the current impl, it means ENDS WITH '%escape' but we want SASI
to understand the %% as an escape for % so the goal is that SASI
understands LIKE '%%escape' as EQUALS TO '%escape'. Am I correct ?

"Moreover all terms that contains single ‘%’ somewhere in the middle should
cause an exception."

--> Not necessarily, sometime people may want to search text pattern
containing the literal %. Imagine the text "this year the average income
has increase by 10%". People may want to search for "10%".


"BUT may be it’s better to make escaping more universal to support a future
possible case where a wildcard could be placed in the middle of a term too?"

--> I guess universal escaping for % is the cleaner and better solution.
However it may involve some complex regular expression. I'm not sure that
input.replaceAll("%%", "%") trick would work for any cases.

And we also need to define when we want to detect operation type
(LIKE_PREFIX, LIKE_SUFFIX, LIKE_CONTAINS, EQUAL) ?

Should we detect operation type BEFORE escaping or AFTER escaping ?





On Mon, Sep 26, 2016 at 3:54 PM, Mikhail Krupitskiy <
mikhail.krupitskiy@jetbrains.com> wrote:

> LIKE '%%%escape' --> EQUALS TO '%%escape' ???
>
> In the current implementation (‘%’ could be a wildcard only at the
> start/end of a term) I guess it should be ’ENDS with ‘%escape’ ‘.
> Moreover all terms that contains single ‘%’ somewhere in the middle should
> cause an exception.
> BUT may be it’s better to make escaping more universal to support a future
> possible case where a wildcard could be placed in the middle of a term too?
>
> Thanks,
> Mikhail
>
> On 24 Sep 2016, at 21:09, DuyHai Doan <doanduyhai@gmail.com> wrote:
>
> Reminder, right now, the % character is only interpreted as wildcard IF
> AND ONLY IF it is the first/last character of the searched term
>
>
> LIKE '%escape' --> ENDS WITH 'escape'
>
> If we use % to escape %,
> LIKE '%%escape' -->  EQUALS TO '%escape'
>
> LIKE '%%%escape' --> EQUALS TO '%%escape' ???
>
>
>
>
> On Fri, Sep 23, 2016 at 5:02 PM, Mikhail Krupitskiy <
> mikhail.krupitskiy@jetbrains.com> wrote:
>
>> Hi, Jim,
>>
>> What pattern should be used to search “ends with  ‘%escape’ “ with your
>> conception?
>>
>> Thanks,
>> Mikhail
>>
>> On 22 Sep 2016, at 18:51, Jim Ancona <jim@anconafamily.com> wrote:
>>
>> To answer DuyHai's question without introducing new syntax, I'd suggest:
>>
>> LIKE '%%%escape' means STARTS WITH '%' AND ENDS WITH 'escape'
>>
>> So the first two %'s are translated to a literal, non-wildcard % and the
>> third % is a wildcard because it's not doubled.
>>
>> Jim
>>
>> On Thu, Sep 22, 2016 at 11:40 AM, Mikhail Krupitskiy <
>> mikhail.krupitskiy@jetbrains.com> wrote:
>>
>>> I guess that it should be similar to how it is done in SQL for LIKE
>>> patterns.
>>>
>>> You can introduce an escape character, e.g. ‘\’.
>>> Examples:
>>> ‘%’ - any string
>>> ‘\%’ - equal to ‘%’ character
>>> ‘\%foo%’ - starts from ‘%foo’
>>> ‘%%%escape’ - ends with ’escape’
>>> ‘\%%’ - starts from ‘%’
>>> ‘\\\%%’ - starts from ‘\%’ .
>>>
>>> What do you think?
>>>
>>> Thanks,
>>> Mikhail
>>>
>>> On 22 Sep 2016, at 16:47, DuyHai Doan <doanduyhai@gmail.com> wrote:
>>>
>>> Hello Mikhail
>>>
>>> It's more complicated that it seems
>>>
>>> LIKE '%%escape' means  EQUAL TO '%escape'
>>>
>>> LIKE '%escape' means ENDS WITH 'escape'
>>>
>>> What's about LIKE '%%%escape' ????
>>>
>>> How should we treat this case ? Replace %% by % at the beginning of the
>>> searched term ??
>>>
>>>
>>>
>>> On Thu, Sep 22, 2016 at 3:31 PM, Mikhail Krupitskiy <
>>> mikhail.krupitskiy@jetbrains.com> wrote:
>>>
>>>> Hi!
>>>>
>>>> We’ve talked about two items:
>>>> 1) ‘%’ as a wildcard in the middle of LIKE pattern.
>>>> 2) How to escape ‘%’ to be able to find strings with the ‘%’ char
with
>>>> help of LIKE.
>>>>
>>>> Item #1was resolved as CASSANDRA-12573.
>>>>
>>>> Regarding to item #2: you said the following:
>>>>
>>>> A possible fix would be:
>>>>
>>>> 1) convert the bytebuffer into plain String (UTF8 or ASCII, depending
>>>> on the column data type)
>>>> 2) remove the escape character e.g. before parsing OR use some advanced
>>>> regex to exclude the %% from parsing e.g
>>>>
>>>> Step 2) is dead easy but step 1) is harder because I don't know if
>>>> converting the bytebuffer into String at this stage of the CQL parser is
>>>> expensive or not (in term of computation)
>>>>
>>>> Let me try a patch
>>>>
>>>> So is there any update on this?
>>>>
>>>> Thanks,
>>>> Mikhail
>>>>
>>>>
>>>> On 20 Sep 2016, at 18:38, Mikhail Krupitskiy <
>>>> mikhail.krupitskiy@jetbrains.com> wrote:
>>>>
>>>> Hi!
>>>>
>>>> Have you had a chance to try your patch or solve the issue in an other
>>>> way?
>>>>
>>>> Thanks,
>>>> Mikhail
>>>>
>>>> On 15 Sep 2016, at 16:02, DuyHai Doan <doanduyhai@gmail.com> wrote:
>>>>
>>>> Ok so I've found the source of the issue, it's pretty well hidden
>>>> because it is NOT in the SASI source code directly.
>>>>
>>>> Here is the method where C* determines what kind of LIKE expression
>>>> you're using (LIKE_PREFIX , LIKE CONTAINS or LIKE_MATCHES)
>>>>
>>>> https://github.com/apache/cassandra/blob/trunk/src/java/org/
>>>> apache/cassandra/cql3/restrictions/SingleColumnRestriction.j
>>>> ava#L733-L778
>>>>
>>>> As you can see, it's pretty simple, maybe too simple. Indeed, they
>>>> forget to remove escape character BEFORE doing the matching so if your
>>>> search is LIKE '%%esc%', the detected expression is LIKE_CONTAINS.
>>>>
>>>> A possible fix would be:
>>>>
>>>> 1) convert the bytebuffer into plain String (UTF8 or ASCII, depending
>>>> on the column data type)
>>>> 2) remove the escape character e.g. before parsing OR use some advanced
>>>> regex to exclude the %% from parsing e.g
>>>>
>>>> Step 2) is dead easy but step 1) is harder because I don't know if
>>>> converting the bytebuffer into String at this stage of the CQL parser is
>>>> expensive or not (in term of computation)
>>>>
>>>> Let me try a patch
>>>>
>>>>
>>>>
>>>> On Wed, Sep 14, 2016 at 9:42 AM, DuyHai Doan <doanduyhai@gmail.com>
>>>> wrote:
>>>>
>>>>> Ok you're right, I get your point
>>>>>
>>>>> LIKE '%%esc%' --> startWith('%esc')
>>>>>
>>>>> LIKE 'escape%%' -->  = 'escape%'
>>>>>
>>>>> What I strongly suspect is that in the source code of SASI, we parse
>>>>> the % xxx % expression BEFORE applying escape. That will explain the
>>>>> observed behavior. E.g:
>>>>>
>>>>> LIKE '%%esc%'  parsed as %xxx% where xxx = %esc
>>>>>
>>>>> LIKE 'escape%%' parsed as xxx% where xxx =escape%
>>>>>
>>>>> Let me check in the source code and try to reproduce the issue
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Sep 13, 2016 at 7:24 PM, Mikhail Krupitskiy <
>>>>> mikhail.krupitskiy@jetbrains.com> wrote:
>>>>>
>>>>>> Looks like we have different understanding of what results are
>>>>>> expected.
>>>>>> I based my understanding on http://docs.datastax.com/en
>>>>>> /cql/3.3/cql/cql_using/useSASIIndex.html
>>>>>> According to the doc ‘esc’ is a pattern for exact match and I
guess
>>>>>> that there is no semantical difference between two LIKE patterns
(both of
>>>>>> patterns should be treated as ‘exact match'): ‘%%esc’ and ‘esc’.
>>>>>>
>>>>>> SELECT * FROM escape WHERE val LIKE '%%esc%'; --> Give all results
>>>>>> *containing* '%esc' so *%esc*apeme is a possible match and also
>>>>>> escape*%esc*
>>>>>>
>>>>>> Why ‘containing’? I expect that it should be ’starting’..
>>>>>>
>>>>>>
>>>>>> SELECT * FROM escape WHERE val LIKE 'escape%%' --> Give all results
>>>>>> *starting* with 'escape%' so *escape%*me is a valid result and also
>>>>>> *escape%*esc
>>>>>>
>>>>>> Why ’starting’? I expect that it should be ‘exact matching’.
>>>>>>
>>>>>> Also I expect that “ LIKE ‘%s%sc%’ ” will return ‘escape%esc’
but it
>>>>>> returns nothing (CASSANDRA-12573).
>>>>>>
>>>>>> What I’m missing?
>>>>>>
>>>>>> Thanks,
>>>>>> Mikhail
>>>>>>
>>>>>> On 13 Sep 2016, at 19:31, DuyHai Doan <doanduyhai@gmail.com>
wrote:
>>>>>>
>>>>>> CREATE CUSTOM INDEX ON test.escape(val) USING '
>>>>>> org.apache.cassandra.index.sasi.SASIIndex' WITH OPTIONS = {'mode':
>>>>>> 'CONTAINS', 'analyzer_class': 'org.apache.cassandra.index.sa
>>>>>> si.analyzer.NonTokenizingAnalyzer', 'case_sensitive': 'false'};
>>>>>>
>>>>>> I don't see any problem in the results you got
>>>>>>
>>>>>> SELECT * FROM escape WHERE val LIKE '%%esc%'; --> Give all results
>>>>>> *containing* '%esc' so *%esc*apeme is a possible match and also
>>>>>> escape*%esc*
>>>>>>
>>>>>> Why ‘containing’? I expect that it should be ’starting’..
>>>>>>
>>>>>>
>>>>>> SELECT * FROM escape WHERE val LIKE 'escape%%' --> Give all results
>>>>>> *starting* with 'escape%' so *escape%*me is a valid result and also
>>>>>> *escape%*esc
>>>>>>
>>>>>> Why ’starting’? I expect that it should be ‘exact matching’.
>>>>>>
>>>>>>
>>>>>> On Tue, Sep 13, 2016 at 5:58 PM, Mikhail Krupitskiy <
>>>>>> mikhail.krupitskiy@jetbrains.com> wrote:
>>>>>>
>>>>>>> Thanks for the reply.
>>>>>>> Could you please provide what index definition did you use?
>>>>>>> With the index from my script I get the following results:
>>>>>>>
>>>>>>> cqlsh:test> select * from escape;
>>>>>>>
>>>>>>>  id | val
>>>>>>> ----+-----------
>>>>>>>   1 | %escapeme
>>>>>>>   2 | escape%me
>>>>>>> *  3 | escape%esc*
>>>>>>>
>>>>>>> Contains search
>>>>>>>
>>>>>>> cqlsh:test> SELECT * FROM escape WHERE val LIKE '%%esc%';
>>>>>>>
>>>>>>>  id | val
>>>>>>> ----+-----------
>>>>>>>   1 | %escapeme
>>>>>>>   3
>>>>>>> * | escape%esc*(2 rows)
>>>>>>>
>>>>>>>
>>>>>>> Prefix search
>>>>>>>
>>>>>>> cqlsh:test> SELECT * FROM escape WHERE val LIKE 'escape%%';
>>>>>>>
>>>>>>>  id | val
>>>>>>> ----+-----------
>>>>>>>   2 | escape%me
>>>>>>>   3
>>>>>>> * | escape%esc*
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Mikhail
>>>>>>>
>>>>>>> On 13 Sep 2016, at 18:16, DuyHai Doan <doanduyhai@gmail.com>
wrote:
>>>>>>>
>>>>>>> Use % to escape %
>>>>>>>
>>>>>>> cqlsh:test> select * from escape;
>>>>>>>
>>>>>>>  id | val
>>>>>>> ----+-----------
>>>>>>>   1 | %escapeme
>>>>>>>   2 | escape%me
>>>>>>>
>>>>>>>
>>>>>>> Contains search
>>>>>>>
>>>>>>> cqlsh:test> SELECT * FROM escape WHERE val LIKE '%%esc%';
>>>>>>>
>>>>>>>  id | val
>>>>>>> ----+-----------
>>>>>>>   1 | %escapeme
>>>>>>>
>>>>>>> (1 rows)
>>>>>>>
>>>>>>>
>>>>>>> Prefix search
>>>>>>>
>>>>>>> cqlsh:test> SELECT * FROM escape WHERE val LIKE 'escape%%';
>>>>>>>
>>>>>>>  id | val
>>>>>>> ----+-----------
>>>>>>>   2 | escape%me
>>>>>>>
>>>>>>> On Tue, Sep 13, 2016 at 5:06 PM, Mikhail Krupitskiy <
>>>>>>> mikhail.krupitskiy@jetbrains.com> wrote:
>>>>>>>
>>>>>>>> Hi Cassandra guys,
>>>>>>>>
>>>>>>>> I use Cassandra 3.7 and wondering how to use ‘%’ as a
simple char
>>>>>>>> in a search pattern.
>>>>>>>> Here is my test script:
>>>>>>>>
>>>>>>>> DROP keyspace if exists kmv;
>>>>>>>> CREATE keyspace if not exists kmv WITH REPLICATION = { 'class'
:
>>>>>>>> 'SimpleStrategy', 'replication_factor':'1'} ;
>>>>>>>> USE kmv;
>>>>>>>> CREATE TABLE if not exists kmv (id int, c1 text, c2 text,
PRIMARY
>>>>>>>> KEY(id, c1));
>>>>>>>> CREATE CUSTOM INDEX ON kmv.kmv  ( c2 ) USING '
>>>>>>>> org.apache.cassandra.index.sasi.SASIIndex' WITH OPTIONS =
{
>>>>>>>> 'analyzed' : 'true',
>>>>>>>> 'analyzer_class' : 'org.apache.cassandra.index.sa
>>>>>>>> si.analyzer.NonTokenizingAnalyzer',
>>>>>>>> 'case_sensitive' : 'false',
>>>>>>>> 'mode' : 'CONTAINS'
>>>>>>>> };
>>>>>>>>
>>>>>>>> INSERT into kmv (id, c1, c2) values (1, 'f22', 'qwe%asd');
>>>>>>>> INSERT into kmv (id, c1, c2) values (2, 'f22', '%asd');
>>>>>>>> INSERT into kmv (id, c1, c2) values (3, 'f22', 'asd%');
>>>>>>>> INSERT into kmv (id, c1, c2) values (4, 'f22', 'asd%1');
>>>>>>>> INSERT into kmv (id, c1, c2) values (5, 'f22', 'qweasd');
>>>>>>>>
>>>>>>>> SELECT c2 from kmv.kmv where c2 like ‘_pattern_';
>>>>>>>>
>>>>>>>> _pattern_ '%%%' finds all columns that contain %.
>>>>>>>> How to find columns that start form ‘%’ or ‘%a’?
>>>>>>>> How to find columns that end with ‘%’?
>>>>>>>> What about more complex patterns: '%qwe%a%sd%’? How to
>>>>>>>> differentiate ‘%’ char form % as a command symbol? (Also
there is a related
>>>>>>>> issue CASSANDRA-12573).
>>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Mikhail
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>

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