Single sql query to select a record from parent table only if all it's records in child table has values

This is called an "anti-join" (or anti-semijoin). One way to write it in SQL is to use the NOT EXISTS construction:

SELECT t1.*
FROM Table1 AS t1
WHERE NOT EXISTS
      ( SELECT *
        FROM Table2 AS t2
        WHERE t2.FKcolumn = t1.PKcolumn
          AND t2.columnX IS NULL
      ) 

If - as your comment - you want a parent row (at Table1) not related to any child row (at Table2), to NOT be shown, add this (or join Table2 if you also want columns from the second table shown):

  AND EXISTS
      ( SELECT *
        FROM Table2 AS t2
        WHERE t2.FKcolumn = t1.PKcolumn
      )