yaooqinn commented on pull request #31940:
URL: https://github.com/apache/spark/pull/31940#issuecomment-805417257
> The PR LGTM.
>
> But I have a quick question, a bit unrelated to this PR but related to
fixed-length string columns. Is this expected that we have in Spark:
>
> ```
> sql(s"CREATE TABLE t(c3 CHAR(3), c5 CHAR(5)) USING parquet")
> sql("INSERT INTO t VALUES ('a', 'a')")
> sql("SELECT c3, c5, c3 = c5, upper(c3) = upper(c5) FROM t").show()
> ```
>
> ```
> +---+-----+---------+-----------------------+
> | c3| c5|(c3 = c5)|(upper(c3) = upper(c5))|
> +---+-----+---------+-----------------------+
> |a |a | true| false|
> +---+-----+---------+-----------------------+
> ```
>
> But in PostgreSQL `upper(c3) = upper(c5)` is true:
>
> ```
> petertoth=# SELECT c3, c5, c3 = c5, upper(c3) = upper(c5) FROM t;
> c3 | c5 | ?column? | ?column?
> -----+-------+----------+----------
> a | a | t | t
> ```
cc @cloud-fan, we seemed to have discussed these when we prohibit
char/varchar in UDFs
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