Question

I have a table named Student as followed:

CREATE TABLE  "STUDENT" 
(   "ID" NUMBER(*,0), 
    "NAME" VARCHAR2(20), 
    "AGE" NUMBER(*,0), 
    "CITY" VARCHAR2(20), 
    PRIMARY KEY ("ID") ENABLE
)

I am trying to get all the records of the students having a larger age than the average age. This is what I tried:

SELECT *
FROM student
WHERE age > AVG(age)

and

SELECT * 
FROM student
HAVING age > AVG(age)

Both ways did not work!

Answer 1

If you going to use an aggregation without a group by you can’t reference other fields. (You are with *)

However you can make a subquery that does.

SELECT *
FROM student
WHERE age > (SELECT AVG(age) FROM STUDENT)

This is easy to write and understand. However if you use analytic functions you can get better performance as Justin Cave explains in his answer