COALESCE (Transact-SQL)
Returns the first nonnull expression among its arguments.
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 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
CREATE TABLE #CheckSumTest
(
ID int identity ,
Num int DEFAULT ( RAND() * 100 ) ,
RowCheckSum AS COALESCE( CHECKSUM( id , num ) , 0 ) PERSISTED PRIMARY KEY
);
14 December 2010
SET NOCOUNT { ON | OFF } in DOT NET
SET NOCOUNT { ON | OFF } in DOT NET
Stops the message indicating the number of rows affected by a Transact-SQL statement from being returned
as part of the results.
Syntax
SET NOCOUNT { ON | OFF }
Remarks
When SET NOCOUNT is ON, the count (indicating the number of rows affected by a Transact-SQL statement)
is not returned. When SET NOCOUNT is OFF, the count is returned.
The @@ROWCOUNT function is updated even when SET NOCOUNT is ON.
SET NOCOUNT ON eliminates the sending of DONE_IN_PROC messages to the client for each statement in a
stored procedure. When using the utilities provided with Microsoft® SQL Server™ to execute queries,
the results prevent "nn rows affected" from being displayed at the end Transact-SQL statements such
as SELECT, INSERT, UPDATE, and DELETE.
For stored procedures that contain several statements that do not return much actual data, this can
provide a significant performance boost because network traffic is greatly reduced.
Stops the message indicating the number of rows affected by a Transact-SQL statement from being returned
as part of the results.
Syntax
SET NOCOUNT { ON | OFF }
Remarks
When SET NOCOUNT is ON, the count (indicating the number of rows affected by a Transact-SQL statement)
is not returned. When SET NOCOUNT is OFF, the count is returned.
The @@ROWCOUNT function is updated even when SET NOCOUNT is ON.
SET NOCOUNT ON eliminates the sending of DONE_IN_PROC messages to the client for each statement in a
stored procedure. When using the utilities provided with Microsoft® SQL Server™ to execute queries,
the results prevent "nn rows affected" from being displayed at the end Transact-SQL statements such
as SELECT, INSERT, UPDATE, and DELETE.
For stored procedures that contain several statements that do not return much actual data, this can
provide a significant performance boost because network traffic is greatly reduced.
4 December 2010
DELEGATES IN C#
DELEGATES IN C#
A delegate type represents references to methods with a particular parameter list and return type.
Delegates make it possible to treat methods as entities that can be assigned to variables and passed as parameters.
Delegates are similar to the concept of function pointers found in some other languages, but unlike function pointers, delegates are object-oriented and type-safe.
The following example declares and uses a delegate type named Function.
using System;
delegate double Function(double x);
class Multiplier
{
double factor;
public Multiplier(double factor) {
this.factor = factor;
}
public double Multiply(double x) {
return x * factor;
}
}
class Test
{
static double Square(double x) {
return x * x;
}
static double[] Apply(double[] a, Function f) {
double[] result = new double[a.Length];
for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);
return result;
}
static void Main() {
double[] a = {0.0, 0.5, 1.0};
double[] squares = Apply(a, Square);
double[] sines = Apply(a, Math.Sin);
Multiplier m = new Multiplier(2.0);
double[] doubles = Apply(a, m.Multiply);
}
}
An instance of the Function delegate type can reference any method that takes a double argument and returns
a double value. The Apply method applies a given Function to the elements of a double[], returning a double[]
with the results. In the Main method, Apply is used to apply three different functions to a double[].
A delegate can reference either a static method (such as Square or Math.Sin in the previous example) or an instance method (such as m.Multiply in the previous example). A delegate that references an instance method also references a particular object, and when the instance method is invoked through the delegate, that object becomes this in the invocation.Delegates can also be created using anonymous functions,which are “inline methods” that are created on the fly. Anonymous functions can see the local variables
of the sourrounding methods. Thus, the multiplier example above can be written more easily without using a Multiplier class:
double[] doubles = Apply(a, (double x) => x * 2.0);
An interesting and useful property of a delegate is that it does not know or care about the class
of the method it references; all that matters is that the referenced method has the same parameters and
return type as the delegate.
A delegate type represents references to methods with a particular parameter list and return type.
Delegates make it possible to treat methods as entities that can be assigned to variables and passed as parameters.
Delegates are similar to the concept of function pointers found in some other languages, but unlike function pointers, delegates are object-oriented and type-safe.
The following example declares and uses a delegate type named Function.
using System;
delegate double Function(double x);
class Multiplier
{
double factor;
public Multiplier(double factor) {
this.factor = factor;
}
public double Multiply(double x) {
return x * factor;
}
}
class Test
{
static double Square(double x) {
return x * x;
}
static double[] Apply(double[] a, Function f) {
double[] result = new double[a.Length];
for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);
return result;
}
static void Main() {
double[] a = {0.0, 0.5, 1.0};
double[] squares = Apply(a, Square);
double[] sines = Apply(a, Math.Sin);
Multiplier m = new Multiplier(2.0);
double[] doubles = Apply(a, m.Multiply);
}
}
An instance of the Function delegate type can reference any method that takes a double argument and returns
a double value. The Apply method applies a given Function to the elements of a double[], returning a double[]
with the results. In the Main method, Apply is used to apply three different functions to a double[].
A delegate can reference either a static method (such as Square or Math.Sin in the previous example) or an instance method (such as m.Multiply in the previous example). A delegate that references an instance method also references a particular object, and when the instance method is invoked through the delegate, that object becomes this in the invocation.Delegates can also be created using anonymous functions,which are “inline methods” that are created on the fly. Anonymous functions can see the local variables
of the sourrounding methods. Thus, the multiplier example above can be written more easily without using a Multiplier class:
double[] doubles = Apply(a, (double x) => x * 2.0);
An interesting and useful property of a delegate is that it does not know or care about the class
of the method it references; all that matters is that the referenced method has the same parameters and
return type as the delegate.
INDEXERS in C#
INDEXERS in C#
An indexer is a member that enables objects to be indexed in the same way as an array. An indexer is declared like a property except that the name of the member is this followed by a parameter list written between the delimiters [ and ]. The parameters are available in the accessor(s) of the indexer. Similar to properties, indexers can be read-write, read-only, and write-only, and the accessor(s) of an indexer can be virtual.
The List class declares a single read-write indexer that takes an int parameter. The indexer makes it possible to index List instances with int values. For example
List names = new List();
names.Add("Liz");
names.Add("Martha");
names.Add("Beth");
for (int i = 0; i < names.Count; i++) {
string s = names[i];
names[i] = s.ToUpper();
}
Indexers can be overloaded, meaning that a class can declare multiple indexers as long as the number or types of their parameters differ.
An indexer is a member that enables objects to be indexed in the same way as an array. An indexer is declared like a property except that the name of the member is this followed by a parameter list written between the delimiters [ and ]. The parameters are available in the accessor(s) of the indexer. Similar to properties, indexers can be read-write, read-only, and write-only, and the accessor(s) of an indexer can be virtual.
The List class declares a single read-write indexer that takes an int parameter. The indexer makes it possible to index List instances with int values. For example
List
names.Add("Liz");
names.Add("Martha");
names.Add("Beth");
for (int i = 0; i < names.Count; i++) {
string s = names[i];
names[i] = s.ToUpper();
}
Indexers can be overloaded, meaning that a class can declare multiple indexers as long as the number or types of their parameters differ.
OUTPUT PARAMETER IN C#
OUTPUT PARAMETER IN C#
An output parameter is used for output parameter passing. An output parameter is similar to a reference parameter except that the initial value of the caller-provided argument is unimportant. An output parameter is declared with the out modifier. The following example shows the use of out parameters.
using System;
class Test
{
static void Divide(int x, int y, out int result, out int remainder) {
result = x / y;
remainder = x % y;
}
static void Main() {
int res, rem;
Divide(10, 3, out res, out rem);
Console.WriteLine("{0} {1}", res, rem); // Outputs "3 1"
}
An output parameter is used for output parameter passing. An output parameter is similar to a reference parameter except that the initial value of the caller-provided argument is unimportant. An output parameter is declared with the out modifier. The following example shows the use of out parameters.
using System;
class Test
{
static void Divide(int x, int y, out int result, out int remainder) {
result = x / y;
remainder = x % y;
}
static void Main() {
int res, rem;
Divide(10, 3, out res, out rem);
Console.WriteLine("{0} {1}", res, rem); // Outputs "3 1"
}
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