I'm playing around with column types and default values, and came across two columns, both smallint but with different defaults:
0(0)::smallintWhen I change 2 to the value 1 has, both are the same and nothing seems changed. Of course, I googled to find the answer to my question, and found that :: is used for type casting. But I wonder, if it is a default value, why would you need type casting?
There is no difference, and the casting is not necessary.
# create table somesmallints (a smallint default 0, b smallint default 0::smallint, c smallint default (0)::smallint);
CREATE TABLE
# \d+ somesmallints;
Table "public.somesmallints"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
--------+----------+-----------+----------+---------------+---------+--------------+-------------
a | smallint | | | 0 | plain | |
b | smallint | | | (0)::smallint | plain | |
c | smallint | | | (0)::smallint | plain | |
# select 0 = 0::smallint;
?column?
----------
t
(1 row)