[jira] [Created] (TAJO-341) Implement substr function

["Hyunsik Choi (JIRA)" <ji...@apache.org>]

Hyunsik Choi created TAJO-341:
---------------------------------

             Summary: Implement substr function
                 Key: TAJO-341
                 URL: https://issues.apache.org/jira/browse/TAJO-341
             Project: Tajo
          Issue Type: New Feature
          Components: operator/function/udf
            Reporter: Hyunsik Choi
            Priority: Minor
             Fix For: 0.8-incubating


h3. Function Definition
{code}
text substr(string text, from int4 [, count int4])
{code}

h3. Description
 * It extracts substring (same as substring(string from from for count)). 
 * If string is null, the result also should be null.
 * Note that *from* is one based index.
 * *from* can be negative integer.
 * *count* can be omitted. If then, all string after *from* will be returned.
 * *count* cannot be negative integer.
 * If *count* is 0, the result should be '' instead of null.

h3. Example and Sementic
{code}
hyunsik=> select substr('abcdef', 3, 2);
 substr 
--------
cd

(1 row)

hyunsik=> select substr('abcdef',3) ;
 substr 
--------
 cdef
(1 row)

hyunsik=> select substr('abcdef',1,1) ;
 substr 
--------
 a

(1 row)
hyunsik=> select substr('abcdef',0,1) ;
 substr 
--------
 
(1 row)

hyunsik=> select substr('abcdef',0,2) ;
 substr 
--------
 a
(1 row)

{code}



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