Select multi column group by one column

Question

Dear SQL Experts,
I have one question related to pl/sql.
I need to do below query. Please advice proper way.
select code, firstname, lastname
from customer
group by code
But group by expecting firstname and lastname.
Please advice
Thank you,
Erdenebayar

Answer 1

Erdenebayar wrote:
I have one question related to pl/sql.You have posted SQL code. Not PL/SQL code.
I need to do below query. Please advice proper way.
select code, firstname, lastname
from customer
group by code
But group by expecting firstname and lastname.Of course you will also need to group by firstname and lastname for that SQL statement.
With a group by SQL you have basically 2 types of values that can be returned:
- the value to group by
- the aggregated/calculated value for that group
So you could look at the first firstname and the last lastname per code:
select
  code, MIN(firstname), MAX(lastname)
from customer
group by codeYou can look at the number of unique first and last names per code:
select
  code, COUNT(DISTINCT firstname), COUNT(DISTINCT lastname)
from customer
group by codeThink of the group by clause in terms of having dimensions (e.g. code in the above SQL) and measures (the calculations per code in the above SQL).