1  时间  
如果是从当前时间到前一个月的这个时候之间的记录总条数：  
select 
count
(1)
  
from 
uis_md_stcustom u
 
where 
firsttime 
between 
add_months(sysdate,-1) 
and 
sysdate;     
如果是求当前时间的前面一个月的内的记录总条数：  
select 
count
(1)
  
from 
uis_md_stcustom u
 
where 
to_char(firsttime,
'mm'
) = to_char(add_months(sysdate,-1),
'mm'
);
    2 IN/ANY  

IN- Equal toany member in the list ANY- Compare value to**each** value returned by the subquery ALL- Compare value to**EVERY** value returned by the subquery <ANY()- less than maximum >ANY()- more than minimum =ANY()- equivalent toIN>ALL()- more than the maximum <ALL()- less than the minimum

eg:

Find the employees who earn the same salary as the minimum salary for each department-

SELECT last_name, salary,department_id FROM employees WHERE salary IN(SELECT MIN(salary)FROM employees GROUPBY department_id);

Employees who are not IT Programmers and whose salary is less than that of any IT programmer-

SELECT employee_id, last_name, salary, job_id FROM employees WHERE salary <ANY(SELECT salary FROM employees WHERE job_id ='IT_PROG')AND job_id <>'IT_PROG';

Employees whose salary is less than the salary ofall employees with a job ID of IT_PROG and whose job is not IT_PROG-

SELECT employee_id,last_name, salary,job_id FROM employees WHERE salary <ALL(SELECT salary FROM employees WHERE job_id ='IT_PROG')AND job_id <>'IT_PROG;