code: private String alterColumnSetNotNull(String tableName, List<String> columnNames) {
          List<String> statement = new ArrayList<>();
          statement.add("ALTER TABLE");
          statement.add(quotize(tableName));
  
          for (String columnName : columnNames) {
              statement.add("ALTER COLUMN");
              statement.add(quotize(columnName));
              statement.add("SET NOT NULL");
          }
  
          return join(statement, " ");
      }
docs: Generates a command to set the specified columns to enforce non nullability.
  
  @param tableName   The table name.
  @param columnNames The columns.
  @return The command to perform the operation.