１.STUFF
将第一个参数，从第start位置开始的length个字符（包含第start位置，位置从１开始），用第四个参数替换。
Syntax

 ( character_expression , start , length ,character_expression )

 Arguments

character_expression

Is an expression of character data. character_expression can be a constant, variable, or column of either character or binary data.

start

Is an integer value that specifies the location to start deletion and insertion. If start or length is negative, a null string is returned. If start is longer than the first character_expression, a null string is returned. start can be of type bigint.

length

Is an integer that specifies the number of characters to delete. If length is longer than the first character_expression, deletion occurs up to the last character in the last character_expression. length can be of type bigint.

 Return Types

Returns character data if character_expression is one of the supported character data types. Returns binary data if character_expression is one of the supported binary data types.

 Remarks

If the start position or the length is negative, or if the starting position is larger than length of the first string, a null string is returned. If the length to delete is longer than the first string, it is deleted to the first character in the first string.

An error is raised if the resulting value is larger than the maximum supported by the return type.

 Examples

The following example returns a character string created by deleting three characters from the first string, abcdef, starting at position 2, at b, and inserting the second string at the deletion point.

SELECT ('abcdef', 2, 3, 'ijklmn');
GO

Here is the result set.

---------
aijklmnef
(1 row(s) affected)

2.COALESCE 
从第一个表达式开始查找非NULL值。找到为止。如果全部为NULL，则返回NULL
Syntax

 ( expression [ ,...n ] ) 

 Arguments

expression

Is an expression of any type.

 Return Types

Returns the data type of expression with the highest data type precedence. If all expressions are nonnullable, the result is typed as nonnullable.

 Remarks

If all arguments are NULL, COALESCE returns NULL.

Note:

At least one of the null values must be a typed NULL.

COALESCE(expression1,...n) is equivalent to the following CASE expression:

CASE

   WHEN (expression1 IS NOT NULL) THEN expression1

   WHEN (expression2 IS NOT NULL) THEN expression2

   ...

   ELSE expressionN

END

ISNULL and COALESCE though equivalent, can behave differently. An expression involving ISNULL with non-null parameters is considered to be NOT NULL, while expressions involving COALESCE with non-null parameters is considered to be NULL. In SQL Server, to index expressions involving COALESCE with non-null parameters, the computed column can be persisted using the PERSISTED column attribute as in the following statement:

Copy Code

CREATE TABLE #CheckSumTest(ID int identity ,Num int DEFAULT ( RAND() * 100 ) ,RowCheckSum AS ( CHECKSUM( id , num ) , 0 ) PERSISTED PRIMARY KEY);

 Examples

Simple Example

The following example demonstrates how COALESCE selects the data from the first column that has a non-null value.

USE AdventureWorks ;

GO

SELECT Name, Class, Color, ProductNumber,

COALESCE(Class, Color, ProductNumber) AS FirstNotNull

FROM Production.Product ;

GO

Complex Example

In the following example, the wages table includes three columns with information about the yearly wages of the employees: the hourly wage, salary, and commission. However, an employee receives only one type of pay. To determine the total amount paid to all employees, use COALESCE to receive only the nonnull value found in hourly_wage, salary, and commission.

Copy Code

SET NOCOUNT ON;
GO
USE tempdb;
IF OBJECT_ID('dbo.wages') IS NOT NULLDROP TABLE wages;
GO
CREATE TABLE dbo.wages
(emp_id        tinyint   identity,hourly_wage   decimal   NULL,salary        decimal   NULL,commission    decimal   NULL,num_sales     tinyint   NULL
);
GO
INSERT dbo.wages (hourly_wage, salary, commission, num_sales)
VALUES
(10.00, NULL, NULL, NULL),
(20.00, NULL, NULL, NULL),
(30.00, NULL, NULL, NULL),
(40.00, NULL, NULL, NULL),
(NULL, 10000.00, NULL, NULL),
(NULL, 20000.00, NULL, NULL),
(NULL, 30000.00, NULL, NULL),
(NULL, 40000.00, NULL, NULL),
(NULL, NULL, 15000, 3),
(NULL, NULL, 25000, 2),
(NULL, NULL, 20000, 6),
(NULL, NULL, 14000, 4);
GO
SET NOCOUNT OFF;
GO
SELECT CAST((hourly_wage * 40 * 52,
salary,
commission * num_sales) AS money) AS 'Total Salary'
FROM dbo.wages
ORDER BY 'Total Salary';
GO

Here is the result set.

Total Salary

------------

20800.0000

41600.0000

62400.0000

83200.0000

10000.0000

20000.0000

30000.0000

40000.0000

45000.0000

50000.0000

120000.0000

56000.0000

(12 row(s) affected)

 See Also

Reference

ISNULL (Transact-SQL)
CASE (Transact-SQL)

Help and Information

Getting SQL Server 2008 Assistance

Navigation

MSDN Library

Azure Services PlatformBing ServicesDesign ToolsDevelopment Tools and LanguagesMobile and Embedded Development.NET DevelopmentOffice DevelopmentOpen Specificationspatterns & practicesServers and Enterprise DevelopmentWeb DevelopmentWin32 and COM Development

Servers and Enterprise Development

ArchitectureSystem CenterBizTalk ServerCommerce ServerConnected Services FrameworkContent Management ServerExchange ServerForefrontHost Integration ServerHyper-VIndustry Solutions GroupInternet Security and Acceleration ...Microsoft DynamicsMicrosoft Enterprise SearchMicrosoft ESPMicrosoft MapPointMicrosoft High Performance Computin...Software TestingSpeech ServerSQL ServerSynchronizationWindows Essential Business ServerWindows Small Business ServerWindows Home ServerWindows Server