ORA-02287: sequence number not allowed here

Question

I am trying to select values from two tables and insert them into one table and calculate the number of placements in total per year. I keep getting an error saying sequence

Answer 1

This query raises the exception:

SELECT cal_id.nextval  , EXTRACT(YEAR FROM start_date) , count(placement_id)
FROM placement
group by year;

This is because you cannot select a sequence value in a query with a group by clause.

Also, a group by clause must include all non-aggregate expressions from the select clause, which yours doesn't. I'm guessing that year is the alias for EXTRACT(YEAR FROM start_date), in which case this is the query you need:

INSERT INTO placement_cal
SELECT cal_id.nextval, year, cnt FROM
( SELECT EXTRACT(YEAR FROM start_date) year, count(placement_id) cnt
  FROM placement
  group by EXTRACT(YEAR FROM start_date)
);