问题
I am trying show all the different companies for which students work. However only companies where more than four students are employed should be displayed.
This is what I have so far:
SELECT EMPLOYER, COUNT (STUDENT_ID)
FROM STUDENT
GROUP BY STUDENT_ID
HAVING COUNT (STUDENT_ID) >4;
I keep getting this message:
ERROR at line 1:
ORA-00979: not a GROUP BY expression
I don't get it. I also tried this earlier:
SELECT STUDENT.EMPLOYER, COUNT (STUDENT.STUDENT_ID)
FROM STUDENT
GROUP BY STUDENT.STUDENT_ID
HAVING COUNT (STUDENT.STUDENT_ID) >4;
but nothing seems to work. Any help is appreciated. I am on SQL*Plus if that helps.
回答1:
Try:
SELECT EMPLOYER, COUNT (STUDENT_ID)
FROM STUDENT
GROUP BY EMPLOYER
HAVING COUNT (STUDENT_ID) >4;
- this will return a list of all employers with more than 4 students.
When grouping or including aggregated fields, your select statement should only include fields that are either aggregated or included in the group by clause - in your existing select, you are including EMPLOYER in your select clause, but not grouping by it or aggregating it.
来源：https://stackoverflow.com/questions/15865146/ora-00979-not-a-group-by-expression