How to add decode but also have count, group by and order by - not a group by expression - oracle

Question

I'm rather new to Oracle. I'm trying to do a count of ports for a vendor/model. However, I only want ones with port_addr_status of 3 or 4. For some reason, I'm getting error
ORA-00979 not a group by expression
This is what I have so far. It works without the decode part, but I don't think the part with pi.port_addr.status in ('3','4') works without it. I'm open to working around that issue as well.
select
count(pi.port) as cnt, d.VENDOR, trim(d.model) as model,
decode(pi.PORT_ADDR_STATUS, '1', 'Unassigned', '2','Pending','3','In Service',
'4','Pending Disco', '5','Trouble', '6','Reserved',
'7','Reserved Capacity', pi.PORT_ADDR_STATUS)
from
table1 pi,
table2 d,
table3 c
where
pi.id = d.id and
pi.circuit_id = c.circuit_id
and pi.port_addr_status in ('3','4')
and (d.dslam_type_desc not in ('AGGREGATOR') or d.dslam_type_desc is null)
and d.DSLAM not like '%#%'
group by
d.VENDOR, d.model --, trim(d.model), pi.RACK, pi.SHELF, pi.SLOT, pi.PORT, pi.BROADBAND_CIRCUIT_ID, d.DSLAM,
order by
d.VENDOR asc, cnt desc
This is sample output:
1031 Adtran TA5000
10 Adtran TA1248V
3 Adtran TA1248

Answer 1

Since the decoded port type is not required in your output, just remove it from the select list. Group By should include everything in the select list except the aggregate functions. The below query should do the job:
select
count(pi.port) as cnt, d.VENDOR, trim(d.model) as model
from
table1 pi,
table2 d,
table3 c
where
pi.id = d.id and
pi.circuit_id = c.circuit_id
and pi.port_addr_status in ('3','4')
and (d.dslam_type_desc not in ('AGGREGATOR') or d.dslam_type_desc is null)
and d.DSLAM not like '%#%'
group by
d.VENDOR, trim(d.model)
order by
d.VENDOR asc, cnt desc
Note that the filter down to specific port types is achieved here:
and pi.port_addr_status in ('3','4')
in the where clause - the decode statement in your original query did nothing to solve your requirements and was the direct cause of the error. In a basic aggregate query like this, group by should have every item that is in the select list that is not an aggregate function.

Answer 2

You might use decode statement in the select list with an aggregation function preferably max as
max( decode(pi.PORT_ADDR_STATUS, '1', 'Unassigned', '2','Pending', .... )

Answer 3

The reason you're getting that error is:
when using a GROUP BY clause you are asking the DBMS to give you a single row corresponding to your GROUP BY list
in your case, you are asking for one row per (Vendor, Model) combination
since each of these rows represents possibly many "underlying" rows (say, e.g. 5 rows for Vendor=A and Model=B), the only other fields you can have in the select list must be aggregates (that's why the "count" field works, it counts the rows, i.e. it can take many row values and return a single value)
the DECODE function is not an aggregate function - it can't "collapse" multiple values into one value (like, say, MAX() can)
It looks to me as if your DECODE function returns strings, so I recommend you aggregate the strings with the LISTAGG function (so if your 5 rows have values of 'asdf', 'fdsa', 'qwer', 'rewq', and 'zxcv' the LISTAGG function would return a single string: 'asdf,fdsa,qwer,rewq,zxcv')
So you would replace your DECODE(...) call with, e.g. LISTAGG(DECODE(...), ',')
Reference for LISTAGG function: https://docs.oracle.com/cd/E11882_01/server.112/e41084/functions089.htm#SQLRF30030