Question

One question about Postgresql selects. This works as it should:

SELECT 
  name,SUM(cash)
FROM 
  costumers
GROUP BY (name)

but how can I concat two (or more) fields in the GROUP BY clause?
This is what I tried:

SELECT 
  name,SUM(cash)
FROM 
  costumers
GROUP BY (name || ' ' || nickname)

Answer 1

That will work, except that you need to select the expression you group by:

SELECT 
    (name || ' ' || nickname) AS name_and_nickname,
    SUM(cash) AS total_cash
FROM costumers
GROUP BY (name || ' ' || nickname)

Another option is to group by two fields by separating them with a comma:

SELECT 
    name, nickname, SUM(cash) AS total_cash
FROM costumers
GROUP BY name, nickname

Note that these two are not exactly equivalent. In particular these two rows will end up in the same group with the first version and in different groups in the second version:

name    | nickname  | cash
--------+-----------+----
foo     | bar baz   | 10
foo bar | baz       | 20

The second option is probably what you mean.