sql missing expression on select query in oracle

Question

I am trying to get rid of duplicate job roles before the data is entered into my actual dimensions table, everytime I run my script I keep getting a missing expression error and im not sure why, any help would be mostly appreciated.

INSERT INTO job_role_dim (
SELECT job_role_id.nextval, DISTINCT job_role_desc
FROM temp_job_role_dim);

Answer 1

You should not have the parentheses around the query, and your distinct is in the wrong place. You're possibly trying to avoid doing this:

INSERT INTO job_role_dim
SELECT DISTINCT job_role_id.nextval,job_role_desc
FROM temp_job_role_dim;

... which doesn't remove the duplicates, but just gives them different sequence values. So you need a subquery:

INSERT INTO job_role_dim
SELECT job_role_id.nextval, job_role_desc
FROM (
  SELECT DISTINCT job_role_desc
  FROM temp_job_role_dim
);

The inline view finds the distinct/unique values; the outer query then gives a sequence value to each of those.

Answer 2

This is an elaboration on Alex's answer. The better way to write this query is using a list of columns for the select. This is generally a really good idea -- and for other reasons than just the parentheses around the query. So:

INSERT INTO job_role_dim(job_role_id, job_role_desc) -- making up these column names
    SELECT job_role_id.nextval, job_role_desc
    FROM (SELECT DISTINCT job_role_desc
          FROM temp_job_role_dim
         ) t;

That is, SQL expects the parentheses after the table to contain a list of columns. And, that is how you should write your INSERT statements. The parser gets confused when you include a subquery, because it is expecting a list of columns.