Oracle PLSQL之HAVING后面的条件可由聚合函数构成，也可由GROUP BY后的字段构成

HAVING主要用于对分组后的数据进行过滤，
一般我们在其后接聚合函数（SUM，COUNT等），
除此之外我们还可以用GROUP BY后面的字段组成HAVING后的过滤条件。
 SQL> select * from dept;

DEPTNO DNAME LOC
------ -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
50 name1 loc1
51 name1 name1
52 loc1 loc1

7 rows selected

SQL> SELECT loc FROM dept GROUP BY loc HAVING count(deptno)>1;

LOC
-------------
loc1

SQL> SELECT loc FROM dept GROUP BY loc HAVING deptno>30;

SELECT loc FROM dept GROUP BY loc HAVING deptno>30

ORA-00979: not a GROUP BY expression

SQL> SELECT loc FROM dept GROUP BY loc,deptno HAVING deptno>30;

LOC
-------------
BOSTON
loc1
loc1
name1

SQL> SELECT loc,deptno FROM dept GROUP BY loc,deptno HAVING deptno>30;

LOC DEPTNO
------------- ------
BOSTON 40
loc1 50
loc1 52
name1 51

SQL>