计算多列中最大值的平均值

Question

I have this table

[1|Sub1|Mark1|Sub2|Mark2|Subj3|Mark3|...]
[2|JSP |85   |ASP |70   |PHP  |95   |...]

I need the average Marks of the two highest subjects?

For example

avg(Mark1,Mark3);

Answer 1

May be are you asking this?

SELECT ID,
  (SELECT AVG(v) 
   FROM (VALUES (Mark1), (Mark2), (Mark3), (Mark4), (Mark5)) AS value(v)) as [AverageMarks]
FROM Table1

If you are looking for only Average of 2 highest subjects among 3 subjects then try this.

SELECT ID,
  (SELECT (SUM(v)-MIN(V))/2
   FROM (VALUES (Mark1), (Mark2), (Mark3)) AS value(v)) as [AverageMarks]
FROM Table1

FIDDLE DEMO

Answer 2

Consider the following:

DROP TABLE IF EXIST my_table;

CREATE TABLE my_table
(subject CHAR(3) PRIMARY KEY
,mark INT NOT NULL
);

INSERT INTO my_table VALUES
('JSP',85),
('ASP',70),
('PHP',95);   

SELECT AVG(a.mark)
  FROM 
     ( SELECT mark FROM my_table ORDER BY mark DESC LIMIT 2 ) a;

+-------------+
| AVG(a.mark) |
+-------------+
|     90.0000 |
+-------------+