What is the purpose of the keyword "ID" in PostgreSQL? I'm new to PostgreSQL and I ran into problems using the following query:

SELECT * FROM table1 WHERE ID = 1



  ERROR:  column "id" does not exist
  LINE 2: WHERE ID = 1


where ID is a column I added via a GUI-tool.
I then found out that ID is a keyword in my current version of PSQL and should be quoted. But I can't recognize what is this ID for.

On the linked page there is the following notice:


  It is important to understand before studying Table C-1 that the fact that a key word is not reserved in PostgreSQL (==true) does not mean that the feature related to the word is not implemented.


So, ID is not marked as a PostgreSQL keyword and there seems to be a feature connected to it, but I can't find out which. SELECT ID itself turns into the same error message as posted above.
In PostgreSQL, inserting a column named

"ID"


is one thing. Inserting a column named 

ID


is another.

create table test (
  "ID" integer not null
);

insert into test values (1);

select *
from test
where ID = 1;

ERROR: column "id" does not exist



  Quoting an identifier also makes it case-sensitive, whereas unquoted
  names are always folded to lower case.