SQLServer常见查询问题

以下语句是在SQLServer2005上实现的,一些语句无法在SS2000上执行。

 

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:
SQL code

--自然数表1-1M
CREATE 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), --2
B2 AS(SELECT n=1 FROM B1 a CROSS JOIN B1 b), --4
B3 AS(SELECT n=1 FROM B2 a CROSS JOIN B2 b), --16
B4 AS(SELECT n=1 FROM B3 a CROSS JOIN B3 b), --256
B5 AS(SELECT n=1 FROM B4 a CROSS JOIN B4 b), --65536
CTE AS(SELECT r=ROW_NUMBER() OVER(ORDER BY (SELECT 1)) FROM B5 a CROSS JOIN B3 b) --65536 * 16
INSERT 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:
SQL code

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
)
GO
WITH 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 Calendar
SELECT
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 END
FROM 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:
SQL code

--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)
) t
CROSS APPLY t.ValuesXML.nodes('/root/v') x(n)



批量的拼接与切分:
SQL code

--测试数据:
CREATE TABLE #ToJoin(
TableName
varchar(20) NOT NULL,
ColumnName
varchar(20) NOT NULL,
PRIMARY KEY CLUSTERED(TableName,ColumnName))
GO
CREATE TABLE #ToSplit(
TableName
varchar(20) NOT NULL PRIMARY KEY CLUSTERED,
ColumnNames
varchar(max) NOT NULL)
GO
INSERT 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')
GO
INSERT 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 t
GROUP 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
) t
CROSS 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。

SQL code

--测试数据
CREATE TABLE #Employees(
EmployeeCode
varchar(20) NOT NULL PRIMARY KEY CLUSTERED,
ReportToCode
varchar(20) NULL)
GO
INSERT 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。

SQL code

--测试数据
CREATE TABLE #IPs(
strIP
varchar(15) NULL,
binIP
binary(4) NULL)
GO
INSERT 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)
GO
SELECT
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(1)) +
CAST(CAST(PARSENAME(strIP,2) AS int) AS binary(1)) +
CAST(CAST(PARSENAME(strIP,1) AS int) AS binary(1)),
intIP_new
= CAST(PARSENAME(strIP,1) AS bigint) +
CAST(PARSENAME(strIP,2) AS bigint) * 256 +
CAST(PARSENAME(strIP,3) AS bigint) * 65536 +
CAST(PARSENAME(strIP,4) AS bigint) * 16777216 --int类型也可以,但浪费空间且不直观
FROM #IPs




6. 中文字符处理
有用指数:★★★★☆

SQLServer中文处理涉及到字符集编码和排序规则,是个非常纠结的问题。参看这篇博客

SQL code

--ASCII字符
SELECT n,x=CAST(n AS binary(2)),u=NCHAR(n) FROM Nums WHERE n BETWEEN 32 AND 126
--UNICODE中文字符
SELECT n,x=CAST(n AS binary(2)),u=NCHAR(n) FROM Nums WHERE n BETWEEN 19968 AND 40869
19968 0x4E00
40869 0x9FA5
--以下两个条件用来判断字符串是否包含汉字
LIKE N'%[吖-咗]%' COLLATE Chinese_PRC_CI_AS
LIKE N'%[一-龥]%' COLLATE Chinese_PRC_BIN
--这是因为在以上两种不同的排序规则下,汉字的排列顺序是不同的。
--
中文全角标点符号
SELECT n,x=CAST(n AS binary(2)),uq=NCHAR(n),ub=NCHAR(n-65248) FROM Nums WHERE n BETWEEN 65281 AND 65374
SELECT NCHAR(12288),NCHAR(32)
65281 0xFF01 ! !
65374 0xFF5E~
--以下条件用来判断字符串是否包含全角标点
LIKE N'%[!-~]%' COLLATE Chinese_PRC_BIN



全角半角标点的转换:
SQL code

--full2half
CREATE FUNCTION [dbo].[full2half](
@String nvarchar(max)
)
RETURNS nvarchar(max)
AS
/*
全角(Fullwidth)转换为半角(Halfwidth)
*/
BEGIN
DECLARE @chr nchar(1)
DECLARE @i int
SET @String = REPLACE(@String,N' ',N' ')
SET @i = PATINDEX(N'%[!-~]%' COLLATE Latin1_General_BIN,@String)
WHILE @i > 0
BEGIN
SET @chr = SUBSTRING(@String,@i,1)
SET @String = REPLACE(@String,@chr,NCHAR(UNICODE(@chr)-65248))
SET @i = PATINDEX(N'%[!-~]%' COLLATE Latin1_General_BIN,@String)
END
RETURN @String
END
GO
CREATE FUNCTION [dbo].[half2full](
@String nvarchar(max)
)
RETURNS nvarchar(max)
AS
/*
半角(Halfwidth)转换为全角(Fullwidth)
*/
BEGIN
DECLARE @chr nchar(1)
DECLARE @i int
SET @String = REPLACE(@String,N' ',N' ')
SET @i = PATINDEX(N'%[!-~]%' COLLATE Latin1_General_BIN,@String)
WHILE @i > 0
BEGIN
SET @chr = SUBSTRING(@String,@i,1)
SET @String = REPLACE(@String,@chr,NCHAR(UNICODE(@chr)+65248))
SET @i = PATINDEX(N'%[!-~]%' COLLATE Latin1_General_BIN,@String)
END
RETURN @String
END
GO

7. binary字符串
有用指数:★☆☆☆☆

0x1234与'0x1234'的相互转换。很明显,CAST/CONVERT是不行的。

SQL code

--string到binary可以用这个系统函数sys.fn_varbintohexstr()(实际上是master.dbo.fn_varbintohexstr)
SELECT sys.fn_varbintohexstr(0x1234),'0x1234'
--binary到string需要自定义函数
CREATE FUNCTION dbo.hexstr2varbin(
@hexstr varchar(max)
)
RETURNS varbinary(max)
AS
/*
将表示16进制的字符串转换为2进制类型
--TESTCASES
SELECT dbo.hexstr2varbin(NULL),NULL
SELECT dbo.hexstr2varbin(''),0x
SELECT dbo.hexstr2varbin('0x'),0x
SELECT dbo.hexstr2varbin('30394161'),0x30394161
SELECT dbo.hexstr2varbin('0x30394161'),0x30394161
SELECT dbo.hexstr2varbin('0x1A2B3C4D5E6F'),0x1A2B3C4D5E6F
SELECT dbo.hexstr2varbin('0x1a2b3c4d5e6f'),0x1a2b3c4d5e6f
--UNIMPLEMENTED
SELECT dbo.hexstr2varbin('0x3039416'),0x3039416
*/
BEGIN
DECLARE @value int
DECLARE @ascii int
DECLARE @varbin varbinary(max)
IF @hexstr LIKE '0x%'
SET @hexstr = STUFF(@hexstr,1,2,'')
SET @hexstr = UPPER(@hexstr)
IF @hexstr NOT LIKE '%[^0-9A-F]%' COLLATE Chinese_PRC_BIN
BEGIN
SET @varbin = 0x
WHILE @hexstr <> ''
BEGIN
SET @value = ASCII(SUBSTRING(@hexstr,1,1))
IF @value <= 57
SET @value = @value - 48
ELSE
SET @value = @value - 55
SET @ascii = @value * 16
SET @value = ASCII(SUBSTRING(@hexstr,2,1))
IF @value <= 57
SET @value = @value - 48
ELSE
SET @value = @value - 55
SET @ascii = @ascii + @value
SET @varbin = @varbin + CAST(@ascii AS binary(1))
SET @hexstr = STUFF(@hexstr,1,2,'')
END
END
RETURN @varbin
END
GO

 

 

posted @ 2011-01-14 10:17 TONYBINLJ 阅读(...) 评论(...) 编辑 收藏