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.
```
BTW, It'll be better to integration testing to compare with postgres
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