pr_table 이 기준이라서 in_table에만 있는건 뺀 쿼리입니다.

select in_code, max(in_pumno), max(in_dcno), sum(in_amt), sum(pr_amt), sum(in_amt) - sum(pr_amt), max(in_vendor) from (
SELECT in_code, in_pumno, in_dcno,  SUM( in_amount ) as in_amt, in_vendor, 0 as pr_amt
FROM in_table
WHERE in_pumno =  '2005173-2'
GROUP BY in_code
union all
SELECT pr_code as in_code, '' as in_pumno, '' as in_dcno, 0 as in_amt,'' as in_vendor, IFNULL( SUM( pr_amount ) , 0 ) AS pr_amt
FROM pr_table
WHERE pr_pumno =  '2005173-2'
and pr_code in(select distinct(in_code) from in_table)
GROUP BY pr_code
) a
group by in_code
order by in_code
LIMIT 30;

3. 쿼리 3

select
  '2005173-2' as in_pumno,
  in_code,
  max(in_dcno),
  sum(in_amt),
  sum(pr_amt),
  sum(in_amt) - sum(pr_amt) as stock,
  max(in_vendor)
from (
  SELECT
    in_code,
    in_dcno,
    SUM(in_amount) as in_amt,
    in_vendor,
    0 as pr_amt
  FROM in_table
  WHERE in_pumno = '2005173-2'
  GROUP BY in_code
  union all
  SELECT
    pr_code as in_code,
    '' as in_dcno,
    0 as in_amt,
    '' as in_vendor,
    IFNULL( SUM( pr_amount ) , 0 ) AS pr_amt
  FROM pr_table
  WHERE pr_pumno = '2005173-2'
  and pr_code in(select distinct(in_code) from in_table)
  GROUP BY pr_code
) T
group by in_code
order by in_code