How to calculate date for weekday and weekend only In Salesforce?

In Salesforce, it is easy to calculate number of day between 2 date.
Just create a formula field, example: End_Date__c - Start_Date__c. DONE!!!

But, is it possible to find out only weekday and only weekend between 2 date?
Hmmm.... most of us will think about Apex Trigger.
Yes, it is correct solution, apex trigger able to calculate without issue, but, if you are not from developer, you need a developer for this.

Wait a minute.... Can we use 'just' formula to calculate weekday and weekend?

YES, it is possible with complex formula. Here we go:

To calculate Weekday
CASE(MOD( Request_Date__c - DATE(2007,1,1),7),
0 , CASE( MOD( Execution_Date__c - Request_Date__c ,7),1,2,2,3,3,4,4,5,5,5,6,5,1),
1 , CASE( MOD( Execution_Date__c - Request_Date__c ,7),1,2,2,3,3,4,4,4,5,4,6,5,1),
2 , CASE( MOD( Execution_Date__c - Request_Date__c ,7),1,2,2,3,3,3,4,3,5,4,6,5,1),
3 , CASE( MOD( Execution_Date__c - Request_Date__c ,7),1,2,2,2,3,2,4,3,5,4,6,5,1),
4 , CASE( MOD( Execution_Date__c - Request_Date__c ,7),1,1,2,1,3,2,4,3,5,4,6,5,1),
5 , CASE( MOD( Execution_Date__c - Request_Date__c ,7),1,0,2,1,3,2,4,3,5,4,6,5,0),
6 , CASE( MOD( Execution_Date__c - Request_Date__c ,7),1,1,2,2,3,3,4,4,5,5,6,5,0),
999)
+ (FLOOR(( Execution_Date__c - Request_Date__c )/7)*5)
-1

To calculate Weekend
CASE(MOD( Request_Date__c - DATE(2007,1,1),7),
0 , CASE( MOD( Execution_Date__c - Request_Date__c, 7),1,0,2,0,3,0,4,0,5,1,6,2,0),
1 , CASE( MOD( Execution_Date__c - Request_Date__c, 7),0,0,1,0,2,0,3,0,4,0,5,2,2),
2 , CASE( MOD( Execution_Date__c - Request_Date__c, 7),0,0,1,0,2,0,3,1,2),
3 , CASE( MOD( Execution_Date__c - Request_Date__c, 7),0,0,1,0,2,1,2),
4 , CASE( MOD( Execution_Date__c - Request_Date__c, 7),0,0,1,1,2),
5 , CASE( MOD( Execution_Date__c - Request_Date__c, 7),0,1,2),
6 , CASE( MOD( Execution_Date__c - Request_Date__c, 7),6,2,1),
999)
+ (FLOOR(( Execution_Date__c - Request_Date__c )/7)*2)

If you see in formula above, we have DATE(2007,1,1), this is refer to 1-Jan-2007 is Monday. So, you can use any date which is Monday, example 1-Jan-1900

Phone Number validation In Salesforce?

Converting 10-Lines of Apex code to a 1-line Validation Rule Formula
Code clean-up is what I'm doing these days ... lots of code clean-up. One of our Salesforce.com orgs (we have sixteen of them) currently has 72% test coverage in production. I'm not sure how the previous administrators were able to install code below the 75% threshold, but they managed. I'm tasked with getting that code cleaned up, so I can deploy a new release.

While looking for areas to improve code coverage, I stumbled upon this trigger:

trigger checkAccountPhoneNumberBiBu on Account (before insert, before update) {
   for (Account account : Trigger.new) {
      if (account.Phone==null) continue;
      Pattern p = Pattern.compile('[-() ]');
      String sPhone = p.matcher(account.Phone).replaceAll('');
      // check length without punctuation
      if (sPhone.length() != 10) account.Phone.addError(' Phone number must have 3 digit area code and 7 digit number');
      p = Pattern.compile('\\d');
      sPhone = p.matcher(sPhone).replaceAll('');
      if (sPhone.length() > 0) account.Phone.addError('Phone number must be formatted as (999)999-9999');
   }
}

This trigger looks at the value entered in the "Phone" field before an Account record is inserted or updated; if the phone field is not in the (999)999-9999 format, it errors out and notifies the user to enter the phone # in the proper format.

In addition to this Apex code, the developer also had to write a testmethod to ensure coverage of the trigger. His code was only getting 67% test coverage (which is what brought the trigger to my attention in the first place).

As I started looking at what I needed to add to the testmethod to ensure 100% coverage, I realized it would be easier to just get rid of the trigger altogether, and replace it with a Validation Rule. That 10 lines of Apex code was reduced to a 1-line formula in a validation rule:

NOT(REGEX(Phone, "\\D*?(\\d\\D*?){10}"))

REQUIRED CHECKBOX VALIDATION?

So we now how to enable a required field in a record, but how about making a requried checkbox in your Salesforce form? well it's simple and here is how to do it:

Field 1: Lookup field called : "Account" Field 2: Date field called "Date" Field 3: Date field called "Expected Completion Date" Field4: Checkbox called "Review"" AND(Review__c = FALSE, OR( NOT(ISBLANK(Account__c)), NOT(ISBLANK(Date__c)), NOT(ISBLANK(Expected_Completion__Date__c))))

and now, If the user enters data in to any one, any two, or all three fields, but does NOT check the box, an error will be thrown.