[GitHub] [arrow-datafusion] xudong963 edited a comment on pull request #1621: feat: Support Substring(str [from int] [for int])

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xudong963 edited a comment on pull request #1621:
URL: https://github.com/apache/arrow-datafusion/pull/1621#issuecomment-1018217879


   Hi, @ovr I do some case tests with Postgres in my local. The followings are some differences.
   
   ```
   // postgres
   postgres=# select * from t;
     a
   -----
    123
   (1 row)
   
   postgres=#  select substring(a,0,3) from t;
    substring
   -----------
    12
   (1 row)
   
   postgres=#  select substring(a,-1, 3) from t;
    substring
   -----------
    1
   (1 row)
   
   // datafusion:pr1621
   ❯ select * from t;
   +-----+
   | c   |
   +-----+
   | 123 |
   +-----+
   1 row in set. Query took 0.009 seconds.
   
   ❯ select substring(c,0,3) from t;
   +-------------------------------+
   | substr(t.c,Int64(0),Int64(3)) |
   +-------------------------------+
   | 123                           |
   +-------------------------------+
   
   ❯ select substring(c,-1,3) from t;
   +--------------------------------+
   | substr(t.c,Int64(-1),Int64(3)) |
   +--------------------------------+
   | 123                            |
   +--------------------------------+
   1 row in set. Query took 0.010 seconds.
   ```


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