A Review of BuiltIn TransactSQL Functions 

StringBased Functions 
Introduction 
The string is the most basic, the primary value that is presented to a database. This is because, any value, before being treated particularly, is firstly considered a string. In an application, there are various ways you use or get a string. You can get it or provide it to a function as a constant string, that is, a string whose value you know certainly and that you pass to a function. You can also get a string that a user provides. Other functions also can produce or return a string.
To assist you with managing strings or performing operations on them, TransactSQL provides various functions. The functions are divided in categories that include characterbased, conversions, addition, substrings, etc.
The Length of a String 
Some operations performed on strings require that you know the number of characters of a string. This is because some operations require a minimum number of characters and some other functions require that the string have at least one character. The number of characters of a string is also called the length of the string.
To get the length of a string, you can use the LEN() function. Its syntax is:
int LEN(String)
This function takes one argument as the string to be considered. It returns the number of characters in the string. Here is an example:
using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Data.SqlClient; namespace Exercise6 { public partial class Exercise : Form { public Exercise() { InitializeComponent(); } private void btnDatabase_Click(object sender, EventArgs e) { SqlConnection connection = new SqlConnection("Data Source=(local);" + "Database='Exercise1';" + "Integrated Security=yes;"); SqlCommand command = new SqlCommand("DECLARE @FIFA varchar(120) " + "SET @FIFA = 'Fédération Internationale de Football Association' " + "SELECT @FIFA, LEN(@FIFA);", connection); connection.Open(); SqlDataReader rdr = command.ExecuteReader(); while (rdr.Read()) { MessageBox.Show("\"" + rdr[0].ToString() + "\" has " + rdr[1].ToString() + " characters."); } rdr.Close(); connection.Close(); } } }
This would produce:
As you may know already, a string is primarily one or a group of characters. These characters are ASCII values. If you have a string, to get the ASCII code of its leftmost character, you can use the ASCII() function. Its syntax is:
int ASCII(String)
This function takes as argument as string and returns the ASCII code of the first (the left) character of the string. Here is an example:
DECLARE @ES varchar(100) SET @ES = 'El Salvador' SELECT @ES AS ES SELECT ASCII(@ES) AS [In ASCII Format]
If you have the ASCII code of a character and want to find its actual character, you can use the CHAR() function. Its syntax is:
char CHAR(int value)
This function takes as argument a numeric value as an integer. Upon conversion, the function returns the ASCII equivalent of that number.
As you may know already, a string can be made of uppercase, lowercase, and symbols that don't have a particular case. When you receive a string, if you want to convert all of its characters to lowercase, you can use the LOWER() function. Its syntax is:
varchar LOWER(String)
This function takes as argument a string. Any lowercase letter that is part of the string would not change. Any letter that is part of the string would be converted to lowercase. Any other character or symbol would be kept "as is". After conversion, the LOWER() function returns a new string.
Here is an example:
private void btnDatabase_Click(object sender, EventArgs e) { SqlConnection connection = new SqlConnection("Data Source=(local);" + "Database='Exercise1';" + "Integrated Security=yes;"); SqlCommand command = new SqlCommand("DECLARE @FIFA varchar(120) " + "SET @FIFA = 'Fédération Internationale de Football Association' " + "SELECT @FIFA, LOWER(@FIFA);", connection); connection.Open(); SqlDataReader rdr = command.ExecuteReader(); while (rdr.Read()) { MessageBox.Show("Original: " + rdr[0].ToString() + "\nConverted: " + rdr[1].ToString()); } rdr.Close(); connection.Close(); }
This would produce:
Remember that the LOWER() function returns a string. Therefore, you can add its result to another call of the function using the + operator. Here is an example:
 =============================================  Function: GetUsername  ============================================= CREATE FUNCTION GetUsername (@FirstName varchar(40), @LastName varchar(40)) RETURNS varchar(50) AS BEGIN DECLARE @Username AS varchar(50); SELECT @Username = LOWER(@FirstName) + LOWER(@LastName); RETURN @Username; END GO
You can then call the function as follows:
SELECT Exercise1.dbo.GetUsername('Francine', 'Moukoko'); GO
A substring is a section gotten from a string. The idea is to isolate one or a group of characters for any necessary reason.
A left substring is one or a group of characters retrieved from the left side of a known string. To get the left substring of a string, you can use the LEFT() function. Its syntax is:
varchar LEFT(String, NumberOfCharacters)
This function takes two arguments. The first argument specifies the original string. The second argument specifies the number of characters from the mostleft that will constitute the substring. After the operation, the LEFT() function returns a new string made of the left character + the NumberOfCharacters on its right from the String.
Here is an example:
using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Data.SqlClient; namespace Exercise6 { public partial class Exercise : Form { public Exercise() { InitializeComponent(); } private void btnCreateUsername_Click(object sender, EventArgs e) { string FirstName, LastName; FirstName = txtFirstName.Text; LastName = txtLastName.Text; SqlConnection connection = new SqlConnection("Data Source=(local);" + "Database='Exercise1';" + "Integrated Security=yes;"); SqlCommand command = new SqlCommand("DECLARE @FirstName varchar(40), " + " @LastName varchar(40), " + " @Username AS varchar(50); " + "SET @FirstName = '" + FirstName + "'; " + "SET @LastName = '" + LastName + "'; " + "SET @Username = LOWER(LEFT(@FirstName, 1)) + " + "LEFT(LOWER(@LastName), 4) " + "SELECT @Username;", connection); connection.Open(); SqlDataReader rdr = command.ExecuteReader(); while (rdr.Read()) { txtUsername.Text = rdr[0].ToString(); } rdr.Close(); connection.Close(); } private void btnClose_Click(object sender, EventArgs e) { Close(); } } }
Here is an example of running the program:
Instead of the starting characters of a string, you may want to create a string using the mostright characters of an existing string. To support this operation, TransactSQL provides the RIGHT() function. Its syntax is:
varchar RIGHT(String, NumberOfCharacters)
This function takes two arguments. The first argument specifies the original string. The second argument specifies the number of characters from the mostright that will constitute the substring.
Here is an example:
 =============================================  Function: Last4DigitsOfSSN  ============================================= CREATE FUNCTION Last4DigitsOfSSN(@SSN varchar(12)) RETURNS char(4) AS BEGIN RETURN RIGHT(@SSN, 4); END GO
You can call the above function as follows:
SELECT Exercise1.dbo.Last4DigitsOfSSN('836483846'); GO
SubStrings: Replacing Occurrences in a String 
One of the most annoying situations you may encounter with a string is to deal with one that contains unexpected characters. This could be due to its formatting or any other reason. For example, if you request a telephone number from a user, there are various ways the string could be presented to you. Examples are 0000000000, or 0000000000, or (000) 0000000. Every one of these formats is an acceptable US and Canadian telephone number but if you involve that string in an operation, you could get an unpredictable result. One way you can solve this type of problem is to remove any undesired characters from the string. This operation can also consist of replacing some character(s) with other(s).
To replace one character or a substring from a string, you can use the REPLACE() function. Its syntax is:
varchar REPLACE(String, FindString, ReplaceWith)
or
binary REPLACE(String, FindString, ReplaceWith)
This function takes three arguments. The first is the string that will be used as reference. The second argument, FindString, is a character or a substring to look for in the String argument. If the FindString character or substring is found in the String, then it is replaced with the value of the last argument, ReplaceWith.
Here is an example:
 =============================================  Function: Last4DigitsOfSSN  ============================================= CREATE FUNCTION Last4DigitsOfSSN(@SSN varchar(12)) RETURNS char(4) AS BEGIN DECLARE @StringWithoutSymbol As varchar(12);  First remove empty spaces SET @StringWithoutSymbol = REPLACE(@SSN, ' ', '');  Now remove the dashes "" if they exist SET @StringWithoutSymbol = REPLACE(@StringWithoutSymbol, '', ''); RETURN RIGHT(@StringWithoutSymbol, 4); END GO
You can call the above function as follows:
SELECT Exercise1.dbo.Last4DigitsOfSSN('244048502'); GO
Arithmetic Functions 
The Sign of a Number 
In arithmetic, a number is considered as being negative (less than 0), null (equal to 0), or positive (higher than 0). When a number is negative, it must have a  symbol to its left. If it is positive, it may display a + symbol to its left or it can omit it. A number without the  or + symbol to its left is considered positive, also referred to as unsigned. The symbol that determines whether a number is positive or negative is referred to as its sign. The sign is easily verifiable if you know the number already. In some cases, when a number is submitted to your application, before taking any action, you may need to get this piece of information.
To find out if a value is positive, null, or negative, TransactSQL provides the SIGN() function. Its syntax is:
SIGN(Expression)
This function takes as argument a number or an expression that can be evaluated to a number. The interpreter would then examine the number:
DECLARE @Number As int; SET @Number = 24.75; SELECT SIGN(@Number) AS [Sign of 1058]; GO 
DECLARE @Number As int; SET @Number = 0; SELECT SIGN(@Number) AS [Sign of Number]; GO 
DECLARE @Number As int; SET @Number = 57.05; SELECT SIGN(@Number) AS [Sign of 57.05]; GO 
Based on this, you can use the SIGN() function to find out whether a value is negative, null, or positive: simply pass the value (or a variable) to SIGN() and use a logical operator to check its sign. Here is an example:
 Square Calculation DECLARE @Side As Decimal(10,3), @Perimeter As Decimal(10,3), @Area As Decimal(10,3); SET @Side = 48.126; SET @Perimeter = @Side * 4; SET @Area = @Side * @Side; IF SIGN(@Side) > 0 BEGIN PRINT 'Square Characteristics'; PRINT ''; PRINT 'Side = ' + CONVERT(varchar(10), @Side, 10); PRINT 'Perimeter = ' + CONVERT(varchar(10), @Perimeter, 10); PRINT 'Area = ' + CONVERT(varchar(10), @Area, 10); END; ELSE PRINT 'You must provide a positive value'; GO
Here is an example of executing the statement:
The Absolute Value of a Number 
The decimal numeric system counts from minus infinity to infinity. This means that numbers are usually negative or positive, depending on their position from 0, which is considered as neutral. In some operations, the number considered will need to be only positive even if it is provided in a negative format. The absolute value of a number x is x if the number is (already) positive. If the number is negative, its absolute value is its positive equivalent. For example, the absolute value of 12 is 12, while the absolute value of –12 is 12.
To get the absolute value of a number, you can use the ABS() function. Its syntax is:
ABS(Expression)
This function takes an expression or a number as argument and returns its absolute value. Here is an example:
DECLARE @NumberOfStudents INTEGER; SET @NumberOfStudents = 32; SELECT ABS(@NumberOfStudents) AS [Number of Students]; GO
The Ceiling of a Number 
To get the ceiling of a number, TransactSQL provides the CEILING() function. Its syntax is:
CEILING(Expression)
This function takes as argument a number or an expression that can evaluate to a number. After the conversion, if the function succeeds, it returns a doubleprecision number that is greater than or equal to Expression. Here is an example:
DECLARE @Number1 As Numeric(6, 2), @Number2 As Numeric(6, 2) SET @Number1 = 12.155; SET @Number2 = 24.06; SELECT CEILING(@Number1) AS [Ceiling of 12.155], CEILING(@Number2) AS [Ceiling of –24.06]; GO
The Floor of a Number 
To support finding the floor of a number, TransactSQL provides the FLOOR() function. Its syntax is:
FLOOR(Expression)
The FLOOR() function takes as argument a numeric value or an expression that can be evaluated to a number. If the function succeeds during its conversion, it produces the integer that is the floor of the argument. Here is an example:
DECLARE @Number1 As Numeric(6, 2), @Number2 As Numeric(6, 2); SET @Number1 = 128.44; SET @Number2 = 36.72; SELECT FLOOR(@Number1) AS [Floor of 128.44], FLOOR(@Number2) AS [Floor of –36.72]; GO
The Exponent of a Number 
To calculate the exponential value of a number, TransactSQL provides the EXP() function. Its syntax is:
EXP(Expression)
This function takes one argument as a number or an expression that can be evaluated to a number. Here is an example:
DECLARE @Number As Numeric(6, 2); SET @Number = 6.48; SELECT EXP(@Number) AS [Exponent of 6.48]; G
The Power of a Number 
The power of a number is the value of that number when raised to another number. This is done using the following formula:
ReturnValue = x^{y}
To support finding the power of a number, TransactSQL provides the POWER() function. Its syntax is:
POWER(x, y)
This function takes two required arguments. The first argument, x, is used as the base number to be evaluated. The second argument, y, also called the exponent, will raise x to this value. Here is an example:
DECLARE @x As Decimal(6, 2), @y As Decimal(6, 2); SET @x = 20.38; SET @y = 4.12; SELECT POWER(@x, @y) AS [Power of 20.38 raised to 4.12]; GO
This would produce:
The Natural Logarithm of a Number 
To assist with finding the natural logarithm of a number, TransactSQL provides the LOG() function. Its syntax is:
LOG(Expression)
This function takes one argument as a number or an expression that can evaluate to a number. After the calculation, it returns the natural logarithm of the argument. Here is an example:
DECLARE @Number As Decimal(6, 2); SET @Number = 48.16; SELECT LOG(@Number) AS [Natural Logarithm of 48.16]; GO
The Base10 Logarithm of a Number 
To calculate the base 10 logarithm of a number, TransactSQL provides the LOG10() function. Its syntax is:
LOG10(Expression)
The number to be evaluated is passed as the argument X. The function returns the logarithm on base 10 using the formula:
y = log10x
which is equivalent to
x = 10^{y}
Here is an example:
DECLARE @Number As Decimal(6, 2); SET @Number = 48.16; SELECT LOG10(@Number) AS [Base10 Logarithm of 48.16]; GO
The Square Root 
To support the calculation of a square root, TransactSQL provides the SQRT() function. Its syntax is:
SQRT(Expression)
This function takes one argument as a positive decimal number. If the number is positive, after the calculation, the function returns the square root of x. Here is an example:
DECLARE @Number As Decimal(6, 2); SET @Number = 48.16; SELECT SQRT(@Number) AS [The square root of 48.16 is]; GO
This would produce:
If the number is negative, you would receive an error. Here is an example:
In this case, you can use a control statement to find out whether the Expression is positive. Here is an example:
DECLARE @Number As Decimal(6, 2); SET @Number = 258.4062; IF SIGN(@Number) > 0 PRINT 'The square root of 258.4062 is ' + CONVERT(varchar(12), SQRT(@Number)); ELSE PRINT 'You must provide a positive number'; GO
Here is one example of executing the statement:
Date and Time Based Functions 
Introduction 
Date and time values are highly used in database applications. They involve sales, time sheets, taxes, overtime work, etc. Based on this usefulness, their operations are supported by various libraries you will be using when developing your application. Without being the most elaborate on this issue, TransactSQL provides its own level of support for date and time values.
Before using a date or a time value in a calculation, remember that you must first get it one way or another. You can define a date or a time constant in your application. An example would be '1992/10/28'. You can declare a DateTime or a SmallDateTime variable and initialize it as you see fit. You may get a date or a time from another function. As the last alternative, you may get a date or time from another application or from a user. Once you have an appropriate date, you can use it.
One of the ways you can assist the user with date and time is to get the current date or the current time. For example, if you create a time sheet, when the user starts using it, it would be convenient to fill part of the time sheet with such predictable values.
To get the current date and the current time of the computer that a user is using, you can use the GETDATE() function of TransactSQL. Its syntax is:
GETDATE()
This function simply returns the current date and time of the operating system.
Date/Time Addition 
One of the primary operations you may want to perform on a date or a time value would consist of adding a value to it. To support this operation, TransactSQL provides the DATEADD() function. Its syntax is:
DATEADD(TypeOfValue, ValueToAdd, DateOrTimeReferenced)
The third argument to this function is the value of a date or a time on which the operation will be performed. It can be a constant value in the form of 'year/month/day' for a date or 'hour:minutes AM/PM' for a time.
The second argument is the value that will be added. It should be a constant integer, such as 8, or a floating point value, such as 4.06.
When calling this function, you must first specify the type of value that you want to add. This type is passed as the first argument. It is used as follows:
DECLARE @Anniversary As DateTime; SET @Anniversary = '2002/10/02'; SELECT DATEADD(yy, 4, @Anniversary) AS Anniversary; GO 
DECLARE @NextVacation As DateTime; SET @NextVacation = '2002/10/02'; SELECT DATEADD(Quarter, 2, @NextVacation) AS [Next Vacation]; GO 
DECLARE @SchoolStart As DateTime; SET @SchoolStart = '2004/05/12'; SELECT DATEADD(m, 5, @SchoolStart) AS [School Start]; GO 
In the same way, you can add values as follows:
Type of Value  Abbreviation  As a result 
Year  yy  A number of years will be added to the date value 
yyyy  
quarter  q  A number of quarters of a year will be added to the date value 
Month  m  A number of months will be added to the date value 
mm  
dayofyear  y  A number of days of a year will be added to the date value 
dy  
Day  d  A number of days will be added to the date value 
dd  
Week  wk  A number of weeks will be added to the date value 
ww  
Hour  hh  A number of hours will be added to the time value 
minute  n  A number of minutes will be added to the time value 
mi  
second  s  A number of seconds will be added to the time value 
ss  
millisecond  ms  A number of milliseconds will be added to the time value 
Date/Time Subtraction 
Another regular operation performed on a date or a time value consists of getting the number of units that has elapsed in the range of two dates or two time values. To support this operation, TransactSQL provides the DATEDIFF() function. Its syntax is:
DATEDIFF(TypeOfValue, StartDate, EndDate)
This function takes three arguments. The second argument is the starting date or the starting time of the range to be considered. The third argument is the end or last date or time of the considered range. You use the first argument to specify the type of value you want the function to produce. This argument uses the same value as those of the DATEADD() function:
Type of Value  Abbreviation  As a result 
Year  yy  The function will return the number of years that have elapsed between the start and the end dates 
yyyy  
quarter  q  The function will return the number of quarters of a year that have elapsed between the start and the end dates 
Month  m  The function will return the number of months that have elapsed between the start and the end dates 
mm  
dayofyear  y  The function will return the number of days of a year that have elapsed between the start and the end dates 
dy  
Day  d  The function will return the number of days that have elapsed between the start and the end dates 
dd  
Week  wk  The function will return the number of weeks that have elapsed between the start and the end dates 
ww  
Hour  hh  The function will return the number of hours that have elapsed between the start and the end times or dates 
minute  n  The function will return the number of minutes that have elapsed between the start and the end times or dates 
mi  
second  s  The function will return the number of seconds that have elapsed between the start and the end times or dates 
ss  
millisecond  ms  The function will return the number of milliseconds that have elapsed between the start and the end times or dates 
Here is an example that calculates the number of years that an employees has been with the company:
DECLARE @DateHired As DateTime,; @CurrentDate As DateTime; SET @DateHired = '1996/10/04'; SET @CurrentDate = GETDATE(); SELECT DATEDIFF(year, @DateHired, @CurrentDate) AS [Current Experience]; GO
This would produce:
Lesson Summary 
Exercises 


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