针对开发人员的SQL Server面试问题

问题

在某个时候，我们需要采访高级数据库开发人员，并检查他们的SQL查询知识。在这些情况下，重要的是要提出与他们在该领域的经验相对应的问题，以便能够评估他们的知识是否符合您的期望。此外，面试的时间通常很有限，因此选择一些涵盖该主题主要方面的高级（但不太复杂）问题至关重要。问题的定义应该明确，以便受访者可以专注于解决方案，而不是浪费时间了解要求。另外，我认为表的示例架构应该很简单，以免使候选者结构复杂。

在本文中，将为高级SQL查询面试定义问题，并提供答案。这对面试官以及开发人员提高自己的技能很有用。请注意，这不是完整的数据库面试问题，因为它仅测试查询技能。应该询问与存储过程，函数，触发器，事务等有关的其他问题。

解

在定义问题和提供答案之前，我们需要创建一个示例和简单的环境。假设我们有一个包含2个表“ Item”和“ Sales”的模式。第一个表是项目的描述，第二个表按日期显示了项目的销售额。架构图如下：

 

这些表的结构如下：

USE master
GO

CREATE DATABASE TestDB
GO

USE [TestDB]
GO

--Tables creation
CREATE TABLE [dbo].[Item]
(
   [ItemID]    [int] NOT NULL,
   [ItemCode]  [nchar](5) NOT NULL,
   [ItemPrice] [money] NULL,
   CONSTRAINT  [PK_Item] PRIMARY KEY CLUSTERED (ItemID)
)
CREATE UNIQUE NONCLUSTERED INDEX [UIX_Item_ItemCode] ON [dbo].[Item]([ItemCode] ASC)
 

CREATE TABLE [dbo].[Sales]
(
   [SalesID]  [int] IDENTITY(1,1) NOT NULL,
   [ItemID]   [int] NOT NULL,
   [SoldDate] [date] NOT NULL,
   CONSTRAINT [PK_Sales] PRIMARY KEY CLUSTERED (SalesID)
) 
 
ALTER TABLE [dbo].[Sales]  WITH CHECK ADD  CONSTRAINT [FK_Sales_Item] FOREIGN KEY([ItemID])
REFERENCES [dbo].[Item] ([ItemID])
 
ALTER TABLE [dbo].[Sales] CHECK CONSTRAINT [FK_Sales_Item] 

是示例数据。

-- insert rows into dbo.Item
INSERT [dbo].[Item] ([ItemID], [ItemCode], [ItemPrice]) VALUES (1, N'A0010', 17455.2900)
INSERT [dbo].[Item] ([ItemID], [ItemCode], [ItemPrice]) VALUES (2, N'B0020', 24500.0000)
INSERT [dbo].[Item] ([ItemID], [ItemCode], [ItemPrice]) VALUES (3, N'C0030', 12450.3200)
INSERT [dbo].[Item] ([ItemID], [ItemCode], [ItemPrice]) VALUES (4, N'D0040', 37784.0000)
INSERT [dbo].[Item] ([ItemID], [ItemCode], [ItemPrice]) VALUES (5, N'E0050', 128000.0000)
INSERT [dbo].[Item] ([ItemID], [ItemCode], [ItemPrice]) VALUES (6, N'F0060', 92000.0000)

-- insert rows into dbo.Sales 
SET IDENTITY_INSERT [dbo].[Sales] ON 
 
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (1, 1, CAST(N'2016-01-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (2, 1, CAST(N'2016-02-22' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (3, 3, CAST(N'2016-03-17' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (4, 5, CAST(N'2016-04-01' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (5, 3, CAST(N'2017-01-03' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (6, 1, CAST(N'2017-02-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (7, 2, CAST(N'2016-05-18' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (8, 1, CAST(N'2016-06-22' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (9, 1, CAST(N'2016-07-01' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (10, 4, CAST(N'2017-03-10' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (11, 4, CAST(N'2017-04-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (12, 1, CAST(N'2016-07-01' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (13, 3, CAST(N'2017-05-03' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (14, 1, CAST(N'2017-05-12' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (15, 1, CAST(N'2017-06-09' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (16, 4, CAST(N'2016-08-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (17, 3, CAST(N'2016-09-30' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (18, 2, CAST(N'2016-09-18' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (19, 4, CAST(N'2016-10-22' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (20, 2, CAST(N'2016-10-17' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (21, 6, CAST(N'2016-11-01' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (22, 3, CAST(N'2017-07-23' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (23, 1, CAST(N'2017-07-03' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (24, 1, CAST(N'2017-08-28' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (25, 1, CAST(N'2017-09-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (26, 2, CAST(N'2017-10-03' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (27, 2, CAST(N'2017-10-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (28, 3, CAST(N'2017-11-25' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (29, 1, CAST(N'2017-11-23' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (30, 2, CAST(N'2017-12-24' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (31, 1, CAST(N'2017-12-09' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (32, 3, CAST(N'2019-01-11' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (33, 1, CAST(N'2016-12-13' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (34, 1, CAST(N'2019-02-23' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (35, 4, CAST(N'2019-02-03' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (36, 4, CAST(N'2019-03-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (37, 2, CAST(N'2019-03-28' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (38, 3, CAST(N'2019-04-16' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (39, 4, CAST(N'2019-05-03' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (40, 6, CAST(N'2018-06-01' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (41, 3, CAST(N'2016-12-04' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (42, 3, CAST(N'2018-01-22' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (43, 1, CAST(N'2018-02-01' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (44, 2, CAST(N'2019-07-10' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (45, 3, CAST(N'2019-08-08' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (46, 3, CAST(N'2018-03-20' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (47, 3, CAST(N'2018-04-16' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (48, 4, CAST(N'2019-09-12' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (49, 4, CAST(N'2019-10-18' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (50, 3, CAST(N'2019-11-15' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (51, 2, CAST(N'2019-12-23' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (52, 4, CAST(N'2019-12-02' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (53, 4, CAST(N'2018-05-16' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (54, 3, CAST(N'2018-07-12' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (56, 2, CAST(N'2018-08-16' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (57, 1, CAST(N'2018-09-19' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (58, 1, CAST(N'2018-10-18' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (59, 2, CAST(N'2018-11-11' AS Date))
INSERT [dbo].[Sales] ([SalesID], [ItemID], [SoldDate]) VALUES (60, 1, CAST(N'2018-12-22' AS Date))
 
SET IDENTITY_INSERT [dbo].[Sales] OFF 

问题

定义好方案后，我们准备提出问题了。

1.获取2019年未售出的商品清单（ItemCode，ItemPrice）。

结果：

2.获取仅在2016年出售的商品清单（ItemCode，ItemPrice）。

 

结果：

3.显示每年的销售总额（年，RunningTotalCountofSales）。

结果：

4.在每个季度的单独列（年度，FirstQuarter，SecondQuarter，ThirdQuarter，ForthQuarter）中获取2018年和2019年已售物品的季度计数。

结果：

5.显示每年的已售商品数量，以及上一年的已售商品数量和上一年的销售数量（年，SoldItemsCount，PreviousSoldItemsCount，增长率（％））的增长（百分比）。如果没有有关上一年销售额的信息，请显示0。

 

结果：

6.更新项目表，将价格第三高的项目的价格提高1000。更新后，项目表中的数据如下。

结果：

答案

以下是上述问题的答案。尽管每个任务可以有不同的解决方案，但每个问题只能提供一个答案。如果您有其他解决方案，请在本文结尾的注释中输入它们。

1. 2019年未售出的物品清单。

SELECT i.ItemCode, i.ItemPrice
FROM dbo.Item i
LEFT JOIN dbo.Sales s ON i.ItemID=s.ItemID AND YEAR(s.SoldDate)=2019
WHERE s.SoldDate IS NULL

2.仅在2016年出售的物品清单。

SELECT ItemCode, ItemPrice
FROM dbo.Item 
WHERE ItemID IN
(
   SELECT ItemID
   FROM dbo.Sales
   EXCEPT 
   SELECT ItemID
   FROM dbo.Sales
   WHERE YEAR(SoldDate)<>2016
)

3.每年的总销售额。

SELECT 
   DISTINCT YEAR(SoldDate) AS [Year], 
   COUNT(SalesID) OVER(ORDER BY YEAR(SoldDate)) AS RunningTotalCountofSales
FROM dbo.Sales

4. 2018年和2019年的已售物品季度计数。

SELECT 
   YEAR(SoldDate) AS [Year],
   SUM(CASE WHEN DATEPART(QUARTER, SoldDate)=1 THEN 1 ELSE 0 END) AS FirstQuarter,
   SUM(CASE WHEN DATEPART(QUARTER, SoldDate)=2 THEN 1 ELSE 0 END) AS SecondQuarter,
   SUM(CASE WHEN DATEPART(QUARTER, SoldDate)=3 THEN 1 ELSE 0 END) AS ThirdQuarter,
   SUM(CASE WHEN DATEPART(QUARTER, SoldDate)=4 THEN 1 ELSE 0 END) AS ForthQuarter
FROM dbo.Sales
WHERE YEAR(SoldDate) BETWEEN 2018 AND 2019
GROUP BY YEAR(SoldDate)

5.每年的销售数量和与上一年相比的销售增长。

SELECT 
   [Year],
   SoldItemsCount, 
   ISNULL(LAG(SoldItemsCount) OVER(ORDER BY [Year]),0) AS PreviousSoldItemsCount,
   ISNULL(((SoldItemsCount-LAG(SoldItemsCount) OVER(ORDER BY [Year]))*100)/LAG(SoldItemsCount) OVER(ORDER BY [Year]),0) AS 'Growth(%)'
FROM
(
   SELECT YEAR(SoldDate) AS [Year], COUNT(*) AS SoldItemsCount
   FROM dbo.Sales
   GROUP BY YEAR(SoldDate)
) t

6.将价格第三高的商品更新1000。

UPDATE ItemWith3rdPrice
SET ItemPrice = ItemPrice + 1000
FROM
(
   SELECT TOP 1 ItemID, ItemPrice 
   FROM
      (
      SELECT TOP 3 ItemID, ItemPrice 
      FROM dbo.Item 
      ORDER BY ItemPrice DESC
      ) t
   ORDER BY ItemPrice
) ItemWith3rdPrice 

SELECT * FROM dbo.Item