Formulas, Validation Rules & Roll-ups

Formula fields

Read-only, calculated on the fly, never stored.

// Weighted pipeline (Currency)
Amount * Probability / 100

// Days open (Number) on Case
IF(IsClosed, ClosedDate - CreatedDate, NOW() - CreatedDate)

// Cross-object: Contact → Account (up to 10 relationships away)
Account.Owner.Email

// Text with picklist
CASE(Rating, "Hot", "🔥 Priority", "Warm", "Follow up", "Low")

// Picklist values must use ISPICKVAL / TEXT
IF(ISPICKVAL(StageName, "Closed Won"), "Won", "Open")

Useful functions: IF, CASE, AND, OR, NOT, ISBLANK, BLANKVALUE, TEXT, VALUE, TODAY(), NOW(), ADDMONTHS, LEFT, CONTAINS, HYPERLINK, IMAGE.

Validation rules

The formula describes the error condition — when it evaluates to TRUE, the save is blocked.

// Close date can't be in the past for open deals
AND(NOT(IsClosed), CloseDate < TODAY())

// Amount required once the deal reaches Proposal
AND(ISPICKVAL(StageName, "Proposal/Price Quote"), ISBLANK(Amount))

// Stage can't move backwards from Closed Won
AND(ISCHANGED(StageName), ISPICKVAL(PRIORVALUE(StageName), "Closed Won"))

// Indian PIN code must be 6 digits
AND(NOT(ISBLANK(BillingPostalCode)), NOT(REGEX(BillingPostalCode, "\\d{6}")))

// Only System Administrators may change the Account owner
AND(ISCHANGED(OwnerId), $Profile.Name <> "System Administrator")

Tips:

• Show the error at a field for better UX.
• ISCHANGED / PRIORVALUE work only on edit (not insert); use ISNEW() for insert-only rules.
• Validation rules also block API, Data Loader and Apex saves — remember data loads.
• Bypass pattern: a custom permission checked with $Permission.Bypass_Validation.

Roll-up summary fields

On the master side of a master-detail relationship: COUNT, SUM, MIN, MAX of child records, with optional filter criteria.

Example: Total_Won__c on Account = SUM of Opportunity Amount where Stage = Closed Won. (Account–Opportunity is a special standard relationship that allows this.)

For a lookup relationship you need a record-triggered Flow or an Apex trigger (see the Roll Up Contact Count challenge).

Interview questions

1. Write a validation rule so Close Date can't be in the past. → CloseDate < TODAY() (for open deals).
2. Formula vs roll-up summary? → Formula: values on the same/parent record. Roll-up: aggregate of children (master-detail only).
3. Why does my data load fail after adding a validation rule? → Rules apply to API loads too.