CREATE TEMPORARY TABLE tmp (
   ID SERIAL,
    Class varchar(50),
    FirstName varchar(50),
    Grade decimal(5,1)
);

INSERT INTO tmp (Class, FirstName, Grade)
    VALUES (‘Math’, ‘Bob’, 65);
INSERT INTO tmp (Class, FirstName, Grade)
    VALUES (‘Math’, ‘Joe’, 72);
INSERT INTO tmp (Class, FirstName, Grade)
    VALUES (‘Math’, ‘Sally’, 95);
INSERT INTO tmp (Class, FirstName, Grade)
    VALUES (‘Science’, ‘Bob’, 65);
INSERT INTO tmp (Class, FirstName, Grade)
    VALUES (‘Science’, ‘Joe’, 81);
INSERT INTO tmp (Class, FirstName, Grade)
    VALUES (‘Science’, ‘Sally’, 81);
INSERT INTO tmp (Class, FirstName, Grade)
    VALUES (‘Science’, ‘Mike’, 72);

SELECT
    x.Class,
    CAST(AVG(x.Grade) AS DECIMAL(6,1)) AS Median
FROM
(
    SELECT
    Class,
    FirstName,
    Grade,
    ROW_NUMBER() OVER (
       PARTITION BY Class
       ORDER BY Grade ASC, ID ASC) AS RowAsc,
    ROW_NUMBER() OVER (
       PARTITION BY Class
       ORDER BY Grade DESC, ID DESC) AS RowDesc
    FROM tmp
) AS x
WHERE
    RowAsc IN (RowDesc, RowDesc – 1, RowDesc + 1)
GROUP BY x.Class
ORDER BY x.Class