Date Time Functions in SQL and the Use of Date Time Functions

Date Time functions in SQL

There are various Date time functions available in SQL which allow us to create trigger based on it. Date time function allow us to check whether an input string is a date or not. Also, we can check what’s the day or week number on a specific date using date time function.

Date Time

Let’s check various date time function available with us:

  1. IsDate

The isDate function is used to check whether the input string is a date or not.

Command: Select isDate(“2012-05-30”), it will return 1

If the input string is not a date, the IsDate date time function will return zero.

The isDate function works well on date, time and datetime datatype but not with datetime2 (timestamp with nanoseconds)

2. Day()

This date time function returns the “day number” of the specified input date string.

Command: Select Day(“2012-02-30 02:35:35”) – Returns 30

3. Month()

This sql date time function returns the “month number” of the specified input date string.

Command: Select Month(“2012-02-30 02:35:35”) – Returns 2

4. Day()

This sql date time function returns the “day number” of the specified input date string.

Command: Select Day(“2012-02-30 02:35:35”) – Returns 30

5. DateName()

The DateName() date time function returns a string value while other date time functions return integer value.

There are various attributes that can be used with the DateName() function. let’s me share some examples of it here:

  1. DateTime(Day, “Date value”|”DateTime Value”) – This function returns the day value (exception it is integer)

Command: Select DateTime(Day, “2013-05-23”) – the output will be 2

2. DateTime(WeekDay, “Date value”|”DateTime Value” – This function returns the week day value

Command: Select DateTime(WeekDay, “2013-05-23”) – the output will be Saturday.

3. DateTime(Month, “Date value”|”DateTime Value”)  – It returns the month value as a string

Command: Select DateTime(Month, “2013-05-23”) – the output will be May.

6. Datepart()

The DatePart() function works similar way as DateName function to find out the weekDay. the only difference between DatePart() and DateName() function is Datepart() returns an integer.

e.g. Select DatePart(WeekDay, “2013-05-25”) will return 2 if it is Tuesday

7. DateAdd()

This sql function will add day, month or year according to the specified value.

Command: Select DateAdd(Day|Month|Year, integer value of addition, Date Value)

e.g. Select DateAdd(Day, 10, “2013-05-20”) – This will output “2013-05-30”

Date Diff

8. DateDiff()

This sql function will add day, month or year according to the specified value.

Command: Select DateDiff(Day|Month|Year, Date value 1,Date value 2)

e.g. Select DateAdd(Month, “2013-05-20″,”2013-01-20”) – This will output 4

Cast and Convert Functions in SQL

Cast and convert functions allow you to convert one data type into another.

Syntax of Cast function:

Select cast(Column_name as Data type)

e.g. Select cast(date as nvarchar)

Syntax of Convert function:

Convert function lets you choose style parameter for string values only. The style feature is not available in cast function. By styling I mean a user defined format in which the output is required.

e.g. Select convert(data type, column_name, style)

There are some specific style codes like 103 means : dd/mm/yyyy. Thus the following example:

Select convert(nvarchar, DateOfBirth, 103)

Stored Procedures and String Functions in SQL

Hola friends, let’s understand what are stored procedures and the benefits of using it. I hope you have learnt some basics of SQL before this. Learn basics of SQL in my previous post.

What are Stored Procedures?

Stored procedures are a set of instructions that need to be instructed again and again. In SQL we can save this frequent instructions as a procedure and call them by just their name.

 

Stored Procedures

How to create Stored Procedures?

To create stored procedures, simply use the Create Proc/Procedure Procedure_name command.

We can also pass parameter in a stored procedure. The parameters can be of two type:

1. Input (Used to take input)

2. Output (used to print output) – The output keyword must be specified as output in the description.

One example of the stored procedure is shown in the below image:

 

Stored-Procedure1

Running the Stored Procedures:

The command used to execute a stored procedure is: EXEC|Execute Procedure_name

e.g. Exec HumanResouces.uspFindEmployee “123” (Here 123 is the value for the @BusinessEntityID input parameter.

Stored Procedure with Output Parameter

An example of output parameter is:

Create Proc spGetEmployeeCount

@LastName int

@EmployeeCount Output

As

Begin

Select @EmployeeCount =Count(*) from emp where LastName = @LastName

End

Executing Stored Procedure with Output Parameter:

To execute the stored procedures with output parameters, it is very important to declare the output variable first. To declare the output variable, use the following command:

Declare @OutputVariableName Datatype

Exec Storedprocedurename Input parameter, Output Parameter Out|Output

Print@OutputVariableName

e.g.

Declare @TotalCount Int

Exec spGetEmployeeCount @LastName = “Male”, @TotalCount Out

Print@TotalCount

Benefits of Stored procedures:

  1. The execution plan can be reused

When a normal statement is executed, the path like first few columns are selected, then refined through where clause and then ordered. This is called a kind of execution plan. So, we can save time through stored procedures.

e.g. Select name, gender from Emp

when id IN(12, 14, 15)

order by name

A normal statement if executed with different parameters, use different execution path. However Stored procedures uses the same execution path even with different variable values.

2. Reduced Network Traffic

Since Stored procedures allows code re-usability, the sql instructions takes less time and space while utilizing network bandwidth. Thus network traffic is reduced.

3. Easy Maintainability using Stored Procedures

Maintenance becomes easy. A change in stored procedure is easy rather than finding similar statements at various places and then modifying the code.

4. Code Re-usability

The instruction that will be required again and again need not to be typed again. We just have to create a stored procedure with that statement and this will help us in reusing the code in less time and space.

5. Better Security

The database can be huge and we don’t want everyone to give access to every user in the network. So, build procedures on the specific table to which the user wants access. This way we will be able to provide better security.

6. Avoid SQL Injection Attack

Stored procedures also helps in avoiding SQL injection attacks. To know more about SQL injection attacks, go to the link.

Learn basics of SQL here

String Functions in SQL

  1. Left function:

This string function in sql returns integer values from the left.

command: select left(string, integer count)

e.g. Select left(“abcd”, 3) – Result will be “abc”

2. Right Function

This string function in sql returns integer values from the right of a string/column value.

command: select left(string/column, integer count)

e.g. Select left(“abcd”, 3) – Result will be “bcd”

3. CharIndex

This sql function returns the index of the character value.

command: Select charindex(“a”, “abcd”) – answer would be 1

4. Len

This function the total length of a string or column value of string type.

command e.g. : Select len(“abcd”) – answer would be 4

Note: This sql string function will not count the blank values at the end of a string.

5. Substr

This sql function is used to select a substring value from a string.

Command: select substr(“string value”|column name, position to start, length of fetch character

e.g. Select substr(“abcd”, 1, 3) – answer would be “abc”

We can also choose negative indexing here. A -1 indicates from the right.

6. Replicate

Replicate function replicates a specific string to the specified number of times.

command: Select replicate(“string”, number of times to replicate)

e.g. Select lastname + replicate(“*”,5)

This command will repeat the * five times in lastname. Let’s say the lastname is “John” then the output is: “John*****”

6. Space

This sql function will insert space to the specified number of times between column values.

command: Select Lastname + Space(5) +First name – This command will introduce a 5 character space between first name column value and last name.

7. PatIndex (or Pattern Index)

PatIndex works the same way as charindex by telling the first occurrence. However, PatIndex allows you to use wildcard. You can’t use wildcard with CharIndex.

e.g. Select PatIndex(“aaab”, “abcaaababc”) – The answer would be 4

If it do not find any matched string, the sql string function returns zero.

8. Replace

This string function replaces a string into another one.

Command: Select(String, “value to replace”, replacement value”)

e.g. Select(“abcd.com”, “.com”, “.net”) – The result will be “abcd.net”

9. LTRIM

This string function is used to trim leading blanks from the beginning.

Command e.g. : Select LTRIM(LastName)

10. RTRIM:

This sql function trims the trailing blank values.

e.g. Last Name : “abcd  ”

Select RTRIM(LastName) – the result will be “abcd”

11. ASCII:

This SQL function returns the ASCII code of the string value.

Command: Select ASCII(string value)

e.g. Select ASCII(A) – The answer would be 65

12. CHAR

This SQL function returns the character value from the integer ASCII code.

Command: Select CHAR(Integer value)

e.g. Select CHAR(65) – The answer would be A

13. STUFF

This sql function replaces a specific string value at the specified position by replacing the characters up to length value. It is kind of masking.

Command: Select STUFF(Column, Starting position, length, String to be used as replacement)

e.g. Select STUFF(LastName, 1, 3, “**”)

If the last name is “JohnMarcel”, the output of stuff function will be “***nMarcel”