In PostgreSQL, all the data types in https://www.postgresql.org/docs/9.1/datatype-numeric.html are supported to create such literals. E.g. smallint '1', float '2.3'
It is odd to support 'integer' only in Spark.
Now we don't care too much about Postgrel compatibility, so I suppose we are not going to add full support for all numeric type literals in this form.

cc @HyukjinKwon @cloud-fan @yaooqinn @MaxGekk

+1, LGTM

Looks fine to me, too.

Test build #115531 has finished for PR 26940 at commit 82a33b2.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

Merged to master.

Linked this with SPARK-30125 as well as #26763.