compare values from 2 columns and display the unique values in other column

hello all

let say i have 3 columns

column a is the new entry , column b is the data , and column c is the result

column b is my database actually , column a is the new entry , that i want to compare to column a

so the result will appear in column c

column a is new entry , it have , 14 , MARY , JOHN , 20

column B is my datalist , it have , JOHN , BOB, 14 ,12

so i need the column c showed MARY and 20

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thanks in advance