Why does 4 / 5 = 0?

SQL Server 
 
You may be startled to see the result of this calculation in SQL Server: 
 

SELECT 4 / 5    -----------   0    (1 row(s) affected)

 
This is because SQL Server is performing integer division... which ignores decimals / fractions / remainders. There are a couple of ways you can force the behavior you really want: 
 

SELECT 4.0 / 5    SELECT 4 * 1.0 / 5    SELECT CAST(4 AS DECIMAL(5,1)) / 5

 
Now, you may not like that there are extra decimal places. To handle this, you can use CAST or CONVERT to shift the results to use 2 decimal places: 
 

SELECT CONVERT(DECIMAL(6,2), (4.0 / 5))    SELECT CAST((4 * 1.0 / 5) AS DECIMAL(6,2))

 
You may also want a leading zero, well this is easy too: 
 

SELECT CONVERT(VARCHAR(6), CONVERT(DECIMAL(6,2), (4.0 / 5)))    SELECT CAST(CAST((4 * 1.0 / 5) AS DECIMAL(6,2)) AS VARCHAR(6))

 
There is no formatpercent operator, like we have in VB / VBA. If you want to add percent signs, you have to do it manually: 
 

SELECT CONVERT(VARCHAR(6), CONVERT(DECIMAL(6,2), (4.0 / 5))) + '%'

 
Or, handle it at the client application (SQL Server really shouldn't be used for formatting issues). 
 
VBScript 
 
VBScript has a similar scenario, but you have to set it up to intentionally produce the result. 
 

<%      ' the is the division operator (/):      response.write 4 / 5          ' result: 0.8        response.write "<br>"        ' the is the integer division operator (\):      response.write 4 \ 5           ' result: 0  %>

 
The most useful application I have come across for the integer division operator is when breaking up minutes into hh:mm, e.g.: 
 

<%      x = datediff("n", date(), now())      h = right("00" & x \ 60, 2)      m = right("00" & x mod 60, 2)      response.write h & ":" & m  %>