与您发布的样本数据（作为图像）

SQL> with
  2  t1 (item, spec) as
  3    (select 'A', 'A1-1' from dual union all
  4     select 'B', 'B1-1' from dual union all
  5     select 'C', 'C1-1' from dual union all
  6     select 'AZ','A1-1' from dual union all
  7     select 'BZ','B1-1' from dual union all
  8     select 'CZ','C1-1' from dual
  9    ),
 10  t2 (item, stock) as
 11    (select 'A', 1 from dual union all
 12     select 'B', 2 from dual union all
 13     select 'C', 5 from dual union all
 14     select 'AZ',3 from dual union all
 15     select 'BZ',4 from dual union all
 16     select 'CZ',6 from dual
 17    )

一个选项-产生所需的结果-是 double-join第二个表和第一个表的item列：一次获取MIN库存值，另一次获取MAX库存值：

18  select
 19    min(a.item) item,
 20    a.spec,
 21    min(b.stock) stock1,
 22    max(c.stock) stock2
 23  from t1 a join t2 b on a.item = b.item
 24            join t2 c on a.item = c.item
 25  group by a.spec
 26  order by a.spec;

IT SPEC     STOCK1     STOCK2
-- ---- ---------- ----------
A  A1-1          1          3
B  B1-1          2          4
C  C1-1          5          6

SQL>