jdbc问题，求教答案和原因

Question

(
EMP_ID NUMBER(4) NOT NULL
LAST_NAME VARCHAR2(30) NOT NULL
FIRST_NAME VARCHAR2(30)
DEPT_ID NUMBER(2)
JOB_CAT VARCHAR2(30)
SALARY NUMBER(8,2)
)

which statement shows the maximum salary paid in each job category of each department?_______
　　a. select dept_id, job_cat,max(salary) from employees where salary > max(salary);
　　b. select dept_id, job_cat,max(salary) from employees group by dept_id,job_cat;
　　c. select dept_id, job_cat,max(salary) from employees;
　　d. select dept_id, job_cat,max(salary) from employees group by dept_id;
　　e. select dept_id, job_cat,max(salary) from employees group by dept_id,job_cat,salary;

Answer 1

b.

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这行文字是为了凑十个字符