SQL数据库常见查询问题
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摘自：http://topic.csdn.net/u/20100528/16/f3c160a2-6d97-4e19-8f74-154d34a940d7.html?seed=1574840243&r=65853880#r_65853880
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1. 生成若干行记录
有用指数：★★★★★
常见的问题类型：根据起止日期生成若干个日期、生成一天中的各个时间段
《SQL Server 2005技术内幕：T-SQL查询》作者建议在数据库中创建一个数据表：
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->--自然数表1-1MCREATE TABLE Nums(n int NOT NULL PRIMARY KEY CLUSTERED)--书上介绍了很多种填充方法，以下是最高效的一种，需要SS2005的ROW_NUMBER()函数。WITH B1 AS(SELECT n=1 UNION ALL SELECT n=1), --2B2 AS(SELECT n=1 FROM B1 a CROSS JOIN B1 b), --4B3 AS(SELECT n=1 FROM B2 a CROSS JOIN B2 b), --16B4 AS(SELECT n=1 FROM B3 a CROSS JOIN B3 b), --256B5 AS(SELECT n=1 FROM B4 a CROSS JOIN B4 b), --65536CTE AS(SELECT r=ROW_NUMBER() OVER(ORDER BY (SELECT 1)) FROM B5 a CROSS JOIN B3 b) --65536 * 16INSERT INTO Nums(n)SELECT TOP(1000000) r FROM CTE ORDER BY r
有了这个数字表，可以做很多事情，除上面提到的两个外，还有：生成一批测试数据、生成所有ASCII字符或UNICODE中文字符、等等。
经常有高手使用SELECT number FROM master..spt_values WHERE type = 'P'，这是很妙的方法；但这样只有2048个数字，而且语句太长，不够方便。
总之，一个数字辅助表（10万还是100万根据个人需要而定），你值得拥有。
2. 日历表
有用指数：★★★☆☆
《SQL编程风格》一书建议一个企业的数据库应该创建一个日历表：
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->CREATE TABLE Calendar( date datetime NOT NULL PRIMARY KEY CLUSTERED, weeknum int NOT NULL, weekday int NOT NULL, weekday_desc nchar(3) NOT NULL, is_workday bit NOT NULL, is_weekend bit NOT NULL)GOWITH CTE1 AS( SELECT date = DATEADD(day,n,'19991231') FROM Nums WHERE n <= DATEDIFF(day,'19991231','20201231')),CTE2 AS( SELECT date, weeknum = DATEPART(week,date), weekday = (DATEPART(weekday,date) + @@DATEFIRST - 1) % 7, weekday_desc = DATENAME(weekday,date) FROM CTE1)--INSERT INTO CalendarSELECT date, weeknum, weekday, weekday_desc, is_workday = CASE WHEN weekday IN (0,6) THEN 0 ELSE 1 END, is_weekend = CASE WHEN weekday IN (0,6) THEN 1 ELSE 0 ENDFROM CTE2
这个表可以很容易根据第1条的数字辅助表生成出来。如果经常需要进行日期处理的话，或许会需要这个表。
还可以在这个表中包含一些企业关心的特殊日期，比如开盘日休市日（股票行业）、特殊纪念日和节日、重要员工的生日，等等。这些日期往往是很难计算的，比如中国的法定节假日（农历问题）。
3. 字符串的拼接(Join)与切分(Split)
有用指数：★★★★★
这个问题非常常见！开发中经常需要把一组值以逗号分隔拼接在一个字符串，或是反过来把一个逗号分隔的字符串切分成一组值。
用SS2005对XML的支持可以非常方便地实现这个功能。
单变量的拼接与切分：
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->--将一组查询结果按指定分隔符拼接到一个变量中DECLARE @Datebases varchar(max)SET @Datebases = STUFF(( SELECT ','+name FROM sys.databases ORDER BY name FOR XML PATH('')),1,1,'')SELECT @Datebases--将传入的一个参数按指定分隔符切分到一个表中DECLARE @SourceIDs varchar(max)SET @SourceIDs = 'a,bcd,123,+-*/=,x&y,<key>'SELECT v = x.n.value('.','varchar(10)')FROM ( SELECT ValuesXML = CAST('<root>' + REPLACE((SELECT v = @SourceIDs FOR XML PATH('')),',','</v><v>') + '</root>' AS XML)) tCROSS APPLY t.ValuesXML.nodes('/root/v') x(n)
批量的拼接与切分：
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->--测试数据：CREATE TABLE #ToJoin( TableName varchar(20) NOT NULL, ColumnName varchar(20) NOT NULL, PRIMARY KEY CLUSTERED(TableName,ColumnName))GOCREATE TABLE #ToSplit( TableName varchar(20) NOT NULL PRIMARY KEY CLUSTERED, ColumnNames varchar(max) NOT NULL)GOINSERT INTO #ToJoin VALUES('tblEmployee','EmployeeCode')INSERT INTO #ToJoin VALUES('tblEmployee','EmployeeName')INSERT INTO #ToJoin VALUES('tblEmployee','HireDate')INSERT INTO #ToJoin VALUES('tblEmployee','JobCode')INSERT INTO #ToJoin VALUES('tblEmployee','ReportToCode')INSERT INTO #ToJoin VALUES('tblJob','JobCode')INSERT INTO #ToJoin VALUES('tblJob','JobTitle')INSERT INTO #ToJoin VALUES('tblJob','JobLevel')INSERT INTO #ToJoin VALUES('tblJob','DepartmentCode')INSERT INTO #ToJoin VALUES('tblDepartment','DepartmentCode')INSERT INTO #ToJoin VALUES('tblDepartment','DepartmentName')GOINSERT INTO #ToSplit VALUES('tblDepartment','DepartmentCode,DepartmentName')INSERT INTO #ToSplit VALUES('tblEmployee','EmployeeCode,EmployeeName,HireDate,JobCode,ReportToCode')INSERT INTO #ToSplit VALUES('tblJob','DepartmentCode,JobCode,JobLevel,JobTitle')GO--拼接(Join)，SQL Server 2005的FOR XML扩展可以将一个列表转成一个字串：SELECT t.TableName, ColumnNames = STUFF( (SELECT ',' + c.ColumnName FROM #ToJoin c WHERE c.TableName = t.TableName FOR XML PATH('')), 1,1,'')FROM #ToJoin tGROUP BY t.TableName--切分(Split)，使用SQL Server 2005对XQuery的支持：SELECT t.TableName, ColumnName = c.ColumnName.value('.','varchar(20)')FROM ( SELECT TableName, ColumnNamesXML = CAST('<Root>' + REPLACE((SELECT ColumnName = ColumnNames FOR XML PATH('')),',','</ColumnName><ColumnName>') + '</Root>' AS xml) FROM #ToSplit) tCROSS APPLY t.ColumnNamesXML.nodes('/Root/ColumnName') c(ColumnName)
需要注意的是，倘若分隔符为“;”或者字符串值中包含XML特殊字符（比如&、<、>等等），以上方法可能会无法处理。
4. 树形结构的存储与查询
有用指数：★★★☆☆
数据库设计中常常会遇到需要存储树形结构，比如员工关系表、组织结构表，等等。
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->--测试数据CREATE TABLE #Employees( EmployeeCode varchar(20) NOT NULL PRIMARY KEY CLUSTERED, ReportToCode varchar(20) NULL)GOINSERT INTO #Employees VALUES('A',NULL)INSERT INTO #Employees VALUES('B','A')INSERT INTO #Employees VALUES('C','A')INSERT INTO #Employees VALUES('D','A')INSERT INTO #Employees VALUES('E','B')INSERT INTO #Employees VALUES('F','B')INSERT INTO #Employees VALUES('G','C')INSERT INTO #Employees VALUES('H','D')INSERT INTO #Employees VALUES('I','D')INSERT INTO #Employees VALUES('J','D')INSERT INTO #Employees VALUES('K','J')INSERT INTO #Employees VALUES('L','J')INSERT INTO #Employees VALUES('M','J')INSERT INTO #Employees VALUES('N','K')GO/*可能遇到的查询问题：1. 员工'D'的所有直接下属2. 员工'D'的所有2级以内的下属（包括直接下属和直接下属的下属）3. 员工'N'的所有上级（按报告线顺序列出）4. 员工@EmployeeCode的所有@LevelDown级以内的下属（@EmployeeCode和@LevelDown以变量传入）DECLARE @EmployeeCode varchar(20), @LevelDown int;SET @EmployeeCode = 'D';SET @LevelDown = 2;5. 员工@EmployeeCode的所有@LevelUp级以内的上级（@EmployeeCode和@LevelUp以变量传入）DECLARE @EmployeeCode varchar(20), @LevelUp int;SET @EmployeeCode = 'N';SET @LevelUp = 2;*/--用递归CTE实现员工树形关系表WITH CTE AS( SELECT EmployeeCode, ReportToCode, ReportToDepth = 0, ReportToPath = CAST('/' + EmployeeCode + '/' AS varchar(200)) FROM #Employees WHERE ReportToCode IS NULL UNION ALL SELECT e.EmployeeCode, e.ReportToCode, ReportToDepth = mgr.ReportToDepth + 1, ReportToPath = CAST(mgr.ReportToPath + e.EmployeeCode + '/' AS varchar(200)) FROM #Employees e INNER JOIN CTE mgr ON e.ReportToCode = mgr.EmployeeCode)SELECT * FROM CTE ORDER BY ReportToPath
5. IPv4地址的存储与查询
有用指数：★★☆☆☆
IPv4的地址实际上是一个4字节的数据。点分十进制的字符串表示是为了人工读写方便，但范围比较则是原始二进制形式方便。因此需要实现二者的相互转换。
<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->--测试数据CREATE TABLE #IPs( strIP varchar(15) NULL, binIP binary(4) NULL)GOINSERT INTO #IPs VALUES('0.0.0.0',NULL)INSERT INTO #IPs VALUES('255.255.255.255',NULL)INSERT INTO #IPs VALUES('127.0.0.1',NULL)INSERT INTO #IPs VALUES('192.168.43.192',NULL)INSERT INTO #IPs VALUES('192.168.1.101',NULL)INSERT INTO #IPs VALUES('65.54.239.80',NULL)INSERT INTO #IPs VALUES(NULL,0xB92AEAD3)INSERT INTO #IPs VALUES(NULL,0x2D4B2E53)INSERT INTO #IPs VALUES(NULL,0x31031B0B)INSERT INTO #IPs VALUES(NULL,0x7C2D5F2F)INSERT INTO #IPs VALUES(NULL,0x473E5D31)INSERT INTO #IPs VALUES(NULL,0x90D7D66B)GOSELECT strIP,binIP, strIP_new = CAST(CAST(SUBSTRING(binIP,1,1) AS int) AS varchar(3)) + '.' + CAST(CAST(SUBSTRING(binIP,2,1) AS int) AS varchar(3)) + '.' + CAST(CAST(SUBSTRING(binIP,3,1) AS int) AS varchar(3)) + '.' + CAST(CAST(SUBSTRING(binIP,4,1) AS int) AS varchar(3)), binIP_new = CAST(CAST(PARSENAME(strIP,4) AS int) AS binary(1)) + CAST(CAST(PARSENAME(strIP,3) AS int) AS binary(1color: #0