JAVA下的SQL_System的建立

SELECT   SUM(qty) AS Quantity_of_Books, stor_id 
FROM     sales
GROUP BY stor_id
ORDER BY Quantity_of_Books
GO

如果用户不指定SUM(qty)的名称，则列的名称将成为“无名列”，语句如下：:
SELECT   SUM(qty), stor_id FROM sales
GROUP BY stor_id
ORDER BY SUM(qty)
GO

derived table 用来从其他表中获取数据，用于当前数据库表的查询工作：
USE      pubs
GO
SELECT   t.stor_name
FROM     stores AS t, (SELECT stor_id, COUNT(DISTINCT discounttype)
                         AS d_count
                         FROM     discounts
                         GROUP BY stor_id) AS w
WHERE    t.stor_id = w.stor_id AND
         w.d_count >= 1 
GO

通过关键字ON来找到匹配的记录来连接。下面是使用连接的一个实例操作：
SELECT   f.stor_id, e.discounttype
FROM     stores f JOIN discounts e
ON       f.stor_id = e.stor_id
GO

SELECT   f.stor_id, e.discounttype
FROM     stores f FULL OUTER JOIN discounts e
ON       f.stor_id = e.stor_id
GO

SELECT   f.stor_id, e.discounttype
FROM     stores f LEFT OUTER JOIN discounts e
ON       f.stor_id = e.stor_id
GO

SELECT   e.stor_id, f.discounttype
FROM     stores e RIGHT OUTER JOIN discounts f
ON       e.stor_id = f.stor_id
GO

SELECT   *
FROM     stores
GO
SELECT   *
FROM     sales
GO
SELECT   *
FROM     stores CROSS JOIN sales
GO

SELECT   t.stor_id, r.discounttype
FROM     stores t RIGHT OUTER JOIN discounts r
ON       t.stor_id = r.stor_id
GO