MySQL - How to check whether all values of a given SELECTed row are equals?
SELECT
   column_a
  ,column_b
  ,column_c
  ,column_d
FROM mytable
WHERE column_a = column_b
AND   column_a = column_c
AND   column_a = column_d


ETC.

SQL Fiddle Link

My Notes

CREATE TABLE mytable
(
column_a int,
column_b int,
column_c int,
column_d int
);

INSERT INTO mytable VALUES (1,2,4,7);
INSERT INTO mytable VALUES (6,3,5,6);
INSERT INTO mytable VALUES (5,5,5,5);
INSERT INTO mytable VALUES (7,1,3,4);
INSERT INTO mytable VALUES (3,3,3,3);