純粹

●合併重覆行
select * from A
union
select * from B

●不合併重覆行
select * from A
union all
select * from B

●按某個欄位排序--合併重覆行
select * from
(select * from A
union
select * from B) AS T
order by 欄位名

●按某個欄位排序--不合併重覆行
select * from
(select * from A
union all
select * from B) AS T
order by 欄位名

●GROUP BY 用法一樣

EX：

SELECT CCY, SUM(AMOUNT) FROM (
(SELECT  'CCY' = CURBUY, 'AMOUNT' = SUM(AMTBUY) FROM vw_CCYAMT  GROUP BY CURBUY)
UNION ALL
(SELECT  'CCY' = CURSEL, 'AMOUNT' = (SUM(AMTSEL) * -1) FROM vw_CCYAMT  GROUP BY CURSEL)
) AS T GROUP BY CCY