Question

I know there is an obvious answer to this question, but I’m like a noob trying to remember how to write queries. I have the following table structure in Postgresql:

CREATE TABLE public.table1 (
  accountid BIGINT NOT NULL, 
  rpt_start DATE NOT NULL, 
  rpt_end DATE NOT NULL, 
  CONSTRAINT table1_pkey PRIMARY KEY(accountid, rpt_start, rpt_end)
) 
WITH (oids = false);

CREATE TABLE public.table2 (
  customer_id BIGINT NOT NULL, 
  read VARCHAR(255), 
  CONSTRAINT table2 PRIMARY KEY(customer_id)
) 
WITH (oids = false);

The objective of the query is to display a result set of accountid’s, count of accountid’s in table1 and read from table2. The join is on table1.accountid = table2.customer_id.

The result set should appear as follows:

accountid     count     read
1234          2         100
1235          9         110
1236          1         91

The count column reflect the number of rows in table1 for each accountid. The read column is a value from table2 associated with the same accountid.

Answer 1

select accountid, "count", read
from
    (
        select accountid, count(*) "count"
        from table1
        group by accountid
    ) t1
    inner join
    table2 t2 on t1.accountid = t2.customer_id
order by accountid