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Is Tightly Coupled: In a tightly coupled relationship, the child record can’t exist without any associated parent record
Relates To: A user can select the related object for the lookup relationship.
Child Relationship Name: A user can set any name
Read Only: : A user can make the field as read-only
Required: Lookup field can be set as required
Unique: Lookup field can be set as unique
Sortable: If a user makes a field sortable, then the records can be sorted in the table or listview in ascending or descending order
Help Text: User The user can enter help text for a lookup field
Description: User The user can enter a description for a lookup field