Question

Is there a way to order your table by something that you don’t select in the select clause such as:

Table Example

   Column  |    Type   |
-----------+-----------+
language   | character |
percentage | real      |
id         | integer   |

So I want to ideally do something like this

SELECT DISTINCT language FROM Example ORDER BY percentage DESC;

But this obviously doesn’t work. Is there a way that I can actually get it to order it by the percentage without actually selecting percentage in the SELECT clause?

This query

SELECT DISTINCT language 
FROM countrylanguage 
ORDER BY percentage DESC; 

gives this error message:

ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list
LINE 1: ...T DISTINCT language FROM countrylanguage ORDER BY percentage...

Answer 1

You don’t need to select a column to sort on it.

create table language_pct (
  id integer primary key,
  language varchar(15) not null,
  percentage real not null,
  unique (language)
);

insert into language_pct values
(1, 'English', 15.3),
(2, 'French', 32.108),
(3, 'Russian', 12.88);

select language
from language_pct
order by percentage desc;

French
English
Russian

And if you had two rows for English, each with a different percentage, what would you have the dbms do for select distinct...?