问题
Why does this work
SELECT DISTINCT FIRSTNAME, LASTNAME
FROM books, CUSTOMERS, orders, orderitems
WHERE STATE IN('FL ', 'GA')
GROUP BY orders.order#, firstname, lastname
HAVING SUM(retail*quantity) > 80
but when firstname, lastname is removed from group by it doesn't?
ORA-00979: not a GROUP BY expression
回答1:
In that case where firstname, lastname are removed from the group by, you get that error because you're SELECTing a column(s) that aren't in the GROUP BY expression, or aren't part of an aggregation/function (i.e. MIN, MAX, AVG, and others).
You could also eliminate the DISTINCT as well.
回答2:
As I can guess
First of all GROUP BY operation is performed and then DISTINCT. In GROUP BY clause you must indicate all non-aggregates . For example you are not permitted to do the following:
SELECT FIRST_NAME, LAST_NAME
FROM EMPLOYEES
GROUP BY HIRE_DATE
You should do it by this way:
SELECT FIRST_NAME, LAST_NAME
FROM EMPLOYEES
GROUP BY HIRE_DATE,FIRST_NAME, LAST_NAME
来源：https://stackoverflow.com/questions/5587648/ora-00979-not-a-group-by-expression