Foo meaning in postgresql

Question

I heard that foo is used as a table alias but why is it needed? ex. When I try to run the code on pgadmin4 it doesn work without the foo and says that the subquery inside From must have an alias. ( Think my knowledge with the whole alias is lacking behind )

`

SELECT pcode,
       district_name
  FROM (SELECT pcode,
               district_name,
               CASE WHEN pcode = '4130033' THEN 0
                    WHEN pcode LIKE '413003%' THEN 1
                    WHEN pcode LIKE '41300%'  THEN 2
                    WHEN pcode LIKE '4130%'   THEN 3
                    WHEN pcode LIKE '413%'    THEN 4
                    WHEN pcode LIKE '41%'     THEN 5
                    WHEN pcode LIKE '4%'      THEN 6
                    ELSE NULL END AS hit_code,
               MIN(CASE WHEN pcode = '4130033' THEN 0
                        WHEN pcode LIKE '413003%' THEN 1
                        WHEN pcode LIKE '41300%'  THEN 2
                        WHEN pcode LIKE '4130%'   THEN 3
                        WHEN pcode LIKE '413%'    THEN 4
                        WHEN pcode LIKE '41%'     THEN 5
                        WHEN pcode LIKE '4%'      THEN 6
                        ELSE NULL END) 
                OVER(ORDER BY CASE WHEN pcode = '4130033' THEN 0
                                   WHEN pcode LIKE '413003%' THEN 1
                                   WHEN pcode LIKE '41300%'  THEN 2
                                   WHEN pcode LIKE '4130%'   THEN 3
                                   WHEN pcode LIKE '413%'    THEN 4
                                   WHEN pcode LIKE '41%'     THEN 5
                                   WHEN pcode LIKE '4%'      THEN 6
                                   ELSE NULL END) AS min_code
          FROM PostalCode) Foo
 WHERE hit_code = min_code;

`

Tried without the Foo and didnt work out

Answer 1

It wants to be able to resolve any potential ambiguity in the column names (which requires an alias to do), even if there is no actual ambiguity present.

Note that in v16, the alias will longer be needed if there is no ambiguity.