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An external value that is provided to a
function is called a parameter. A function can also take more than one
parameter. Therefore, when you create a function, you also decide whether
your function would take one or more parameters and what those parameters,
if any, would be.
We have already seen that a function's name is also
followed by parentheses. If the function doesn't use an external value,
its parentheses can be left empty. If a function will use an external
value, when you create the function, you must specify a name and the type
of value of the parameters. The name of the parameter is created with the @
sign, like a variable as we saw in the previous lesson. Here is an example:
CREATE FUNCTION Addition(@Number1 Decimal(6,2))
When a function takes a parameter, in the body of the
function, you can use the parameter as if you knew its value, as long as
you respect the type of that value. Here is an example:
CREATE FUNCTION Addition(@Number1 Decimal(6,2))
RETURNS Decimal(6,2)
BEGIN
RETURN @Number1 + 1450
END
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Calling a Parameterized Function |
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When you call a function that takes one parameter, you
must supply a value for that argument. To do this, type the value of the
parameter in the parentheses of the function. Here is an example:
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A Function With Various Arguments |
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Instead of only one parameter, you can also create a
function that takes more than one parameter. In this case, separate the
arguments in the parentheses of the function with a comma. Here is an
example:
CREATE FUNCTION Addition(@Number1 Decimal(6,2), @Number2 Decimal(6,2))
Once again, in the body of the function, you can use
the parameters as if you already knew their value. You can also declare
local variables and involve them with parameters as you see fit. Here is an
example:
CREATE FUNCTION Addition(@Number1 Decimal(6,2),
@Number2 Decimal(6,2))
RETURNS Decimal(6,2)
BEGIN
DECLARE @Result Decimal(6,2)
SET @Result = @Number1 + @Number2
RETURN @Result
END;
GO
When calling a function that takes more than one
parameter, in the parentheses of the function, provide a value for each
parameter, in the exact order they appear in the parentheses of the
function. Here is an example:
PRINT Variables1.dbo.Addition(1450, 228);
You can also pass the names of already declared and
initialized variables. Here is an example that calls the above function:
DECLARE @Nbr1 Decimal(6,2),
@Nbr2 Decimal(6,2)
SET @Nbr1 = 4268.55
SET @Nbr2 =26.83
SELECT @Nbr1 As First,
@Nbr2 As Second,
Variables1.dbo.Addition(@Nbr1, @Nbr2) AS Result
This would produce:
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 Practical
Learning: Creating and Calling a Function with Argument
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- On the form, double-click the Database button and change its code as
follows:
private void btnDatabase_Click(object sender, EventArgs e)
{
string strConnection =
"Data Source=(local);" +
"Database='UtilityCompany1';" +
"Integrated Security=yes;";
// The following function is used to calculate the customer's next bill
// Some of the empty spaces, not required,
// are meant to make the code easier to read
string CreateFunction = "CREATE FUNCTION EvaluateInvoice(@Counter int) " +
"RETURNS decimal(6, 2) " +
"AS " +
"BEGIN " +
" DECLARE @BaseCharge money, " +
" @Counter0To50 int, " +
" @Counter50To150 int, " +
" @Counter150To200 int, " +
" @CounterOver200 int, " +
" @First50 decimal(6, 2), " +
" @FiftyTo150 decimal(6, 2), " +
" @OneFiftyTo200 decimal(6, 2) ," +
" @Over200 decimal(6, 2), " +
" @TotalCharge money; " +
" SET @BaseCharge = 8.50; " +
" SET @Counter0To50 = 0; " +
" SET @Counter50To150 = 0; " +
" SET @Counter150To200 = 0; " +
" SET @CounterOver200 = 0; " +
" SET @First50 = 0.00; " +
" SET @FiftyTo150 = 0.00; " +
" SET @OneFiftyTo200 = 0.00; " +
" SET @Over200 = 0.00; " +
" SET @TotalCharge = 0.00; " +
" IF @Counter <= 50 " +
" BEGIN" +
" SET @Counter0To50 = @Counter; " +
" SET @Counter50To150 = 0; " +
" SET @Counter150To200 = 0; " +
" SET @CounterOver200 = 0; " +
" END;" +
" IF (@Counter > 50) AND (@Counter <= 150) " +
" BEGIN" +
" SET @Counter0To50 = 50; " +
" SET @Counter50To150 = @Counter - 50; " +
" SET @Counter150To200 = 0; " +
" SET @CounterOver200 = 0; " +
" END;" +
" IF (@Counter > 150) AND (@Counter <= 300) " +
" BEGIN " +
" SET @Counter0To50 = 50; " +
" SET @Counter50To150 = 100; " +
" SET @Counter150To200 = @Counter - 150; " +
" SET @CounterOver200 = 0; " +
" END; " +
" IF @Counter > 300 " +
" BEGIN " +
" SET @Counter0To50 = 50; " +
" SET @Counter50To150 = 100; " +
" SET @Counter150To200 = 100; " +
" SET @CounterOver200 = @Counter - 300; " +
" END;" +
" SET @First50 = @Counter0To50 * 0.7675; " +
" SET @FiftyTo150 = @Counter50To150 * 0.6248; " +
" SET @OneFiftyTo200 = @Counter150To200 * 0.5825; " +
" SET @Over200 = @CounterOver200 * 0.5037; " +
" SET @TotalCharge = @BaseCharge + @First50 + @FiftyTo150 + " +
" @OneFiftyTo200 + @Over200; " +
" RETURN @TotalCharge; " +
"END;";
using (SqlConnection connection = new SqlConnection(strConnection))
{
SqlCommand command =
new SqlCommand(CreateFunction, connection);
connection.Open();
command.ExecuteNonQuery();
MessageBox.Show(
"A function named \"EvaluateInvoice\" has been created.");
}
}
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- Change the code of the Evaluate button as follows:
private void btnEvaluate_Click(object sender, EventArgs e)
{
int StartCounter = 0, EndCounter = 0;
int Consumption;
try
{
StartCounter = int.Parse(txtCounterLastMonth.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Start Counter");
}
try
{
EndCounter = int.Parse(txtCounterThisMonth.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid End Counter");
}
if (StartCounter > EndCounter)
{
MessageBox.Show("Invalid Values");
return;
}
Consumption = EndCounter - StartCounter;
string strConnection =
"Data Source=(local);" +
"Database='UtilityCompany1';" +
"Integrated Security=yes;";
string ExecuteFunction = "DECLARE @Difference int " +
"SET @Difference = " + Consumption.ToString() +
"SELECT dbo.EvaluateInvoice(@Difference);";
using (SqlConnection connection = new SqlConnection(strConnection))
{
SqlCommand command =
new SqlCommand(ExecuteFunction, connection);
connection.Open();
SqlDataReader rdr = command.ExecuteReader();
txtConsumption.Text = Consumption.ToString();
while (rdr.Read())
txtAmountDue.Text = rdr[0].ToString();
rdr.Close();
}
}
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- Execute the application
- Enter some values for the start and end counter
- Click Evaluate. Here is an example:
- Close the form and return to your programming environment
- On the form, double-click the Database button and change the code of
its event as follows:
private void btnDatabase_Click(object sender, EventArgs e)
{
string strConnection =
"Data Source=(local);Integrated Security=yes";
using (SqlConnection connection = new SqlConnection(strConnection))
{
SqlCommand command =
new SqlCommand("DROP DATABASE UtilityCompany1;",
connection);
connection.Open();
command.ExecuteNonQuery();
MessageBox.Show(
"The UtilityCompany1 database has been deleted.");
}
}
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- Execute the application
- Click the Create button
- Close the form and return to your programming environment
- Write a function named ProcessPayroll1 that takes the number of hours
worked in a week. Then the function returns a value that represents
overtime. If the employee worked less than 40 hours, there is no overtime.
If the employee worked for more than 40 hours, the number over 40 is
considered overtime
- Write a function named GetWeekdayName that, when given a date, can find and display the name of
the week for that date
- Write a function named GetNumberDays that takes two dates and returns the
number of days between them
- Write a function named AddNumberDays that takes a date and an integer,
then it returns the date added that number
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