create table ACTUALS
(
  ITEM_NBR   NUMBER,
  ACTUAL_AMT NUMBER,
  CHECK_NBR  CHAR(4)
)
;
create table ESTIMATES
(
  ITEM_NBR      NUMBER,
  ESTIMATED_AMT NUMBER
)
;
create table ITEMS
(
  ITEM_NBR   NUMBER,
  ITEM_DESCR CHAR(7)
)
;
insert into ACTUALS (ITEM_NBR, ACTUAL_AMT, CHECK_NBR)
values (10, 300, '1111');
insert into ACTUALS (ITEM_NBR, ACTUAL_AMT, CHECK_NBR)
values (20, 325, '2222');
insert into ACTUALS (ITEM_NBR, ACTUAL_AMT, CHECK_NBR)
values (20, 100, '3333');
insert into ACTUALS (ITEM_NBR, ACTUAL_AMT, CHECK_NBR)
values (30, 525, '1111');

insert into ESTIMATES (ITEM_NBR, ESTIMATED_AMT)
values (10, 300);
insert into ESTIMATES (ITEM_NBR, ESTIMATED_AMT)
values (10, 50);
insert into ESTIMATES (ITEM_NBR, ESTIMATED_AMT)
values (20, 325);
insert into ESTIMATES (ITEM_NBR, ESTIMATED_AMT)
values (20, 110);
insert into ESTIMATES (ITEM_NBR, ESTIMATED_AMT)
values (40, 25);

insert into ITEMS (ITEM_NBR, ITEM_DESCR)
values (10, 'item 10');
insert into ITEMS (ITEM_NBR, ITEM_DESCR)
values (20, 'item 20');
insert into ITEMS (ITEM_NBR, ITEM_DESCR)
values (30, 'item 30');
insert into ITEMS (ITEM_NBR, ITEM_DESCR)
values (40, 'item 40');
insert into ITEMS (ITEM_NBR, ITEM_DESCR)
values (50, 'item 50');

commit ;

下篇文章 讲一下思路