How to prevent a column from repeating in the final result when using the LISTAGG function

Question

I have a table like this:

CUST_NUMBER | CUST_NAME | CUST_PROFESSION
------------------------------------------  
   1        |   Mike    |    Teacher
   1        |   Mike    |    Engineer
   2        |   Jack    |    Driver
   3        |   Charlie |    Swimmer
   4        |   Negin   |    Engineer
   5        |   Zahara  |    Manager

In want to use the LISTAGG function to produce this result:

  CUST_NUMBER | NAME_PROFESSION
  -----------------------------
       1      | [Mike:Teacher,Engineer]
       2      | [Jack:Driver]
       3      | [Charlie:Swimmer]
       4      | [Negin:Engineer]
       5      | [Zahara:Manager]

What I've written so far is the query below:

select cust_number,
       '['||listagg(cust_name||':'||cust_profession,',')  within group (order by cust_number)||']' Cust_profession 
from CUSTOMER_PROFESSION 
group by cust_number;

The problem I have is that this gives me [Mike:Engineer,Mike:Teacher] (as you can see , the name Mike is repeated) instead of [Mike:Teacher,Engineer] . How can I solve this problem?

Thanks in advance

Answer 1

You want to see employee name out of aggregated professions list - so you must concatenate it to aggregating expression, not to separate profession in arguments.

If do this directly

select cust_number,
       '['||MAX(cust_name)||':'||listagg(cust_profession,',')  within group (order by cust_number)||']' Cust_profession 
from CUSTOMER_PROFESSION 
group by cust_number;

then cust_name become non-grouped, and Oracle produces an error "ORA-00979: not a GROUP BY expression".

This can be solved either by wrapping this column with aggregated function, for example, MAX():

select cust_number,
       '['||MAX(cust_name)||':'||listagg(cust_profession,',')  within group (order by cust_number)||']' Cust_profession 
from CUSTOMER_PROFESSION 
group by cust_number;

or by adding this column into grouping expression (preferred):

select cust_number,
       '['||cust_name||':'||listagg(cust_profession,',')  within group (order by cust_number)||']' Cust_profession 
from CUSTOMER_PROFESSION 
group by cust_number, cust_name;

fiddle