--1
select emp_no from employee where emp_no in (select emp_no from works_on where project_no in (select project_no from project where project_no = 'p2' and emp_no <10000))

--2
select emp_no from works_on where enter_date < '2007-01-01' and enter_date < '2007-12-31'

--3
select emp_no, emp_lname from employee where emp_fname like '%t%t%'

--4
select emp_no from employee where dept_no in(select dept_no from department where location = 'Seattle')
--5
If the grouping column contains a null value,that row becomes a group in the results. If the grouping column contains more than one null value, the null values are put into a single group.

--6
The COUNT(column) function returns the number of values (NULL values will not be counted) of the specified column
The COUNT(*) function returns the number of records in a table

--7
select max(emp_no) from employee

--8
select job from works_on group by job having count(job) > 2

--9
select emp_no,job from works_on where project_no in(select project_no from project where project_name='Gemini')

--10
select emp_fname, emp_lname from employee where dept_no in(select dept_no from department where dept_name = 'Research' or dept_name = 'Accounting')

--11
select enter_date from works_on where emp_no in(select emp_no from employee where dept_no in (select dept_no from department where job='clerk' and dept_no='d1'))

--13
select emp_fname, emp_lname from employee where emp_no in (select emp_no from works_on where project_no in (select project_no from project where project_name='Mercury' and job='manager'))

--14
select emp_no from employee where dept_no in (select dept_no from department where dept_name='marketing')
select emp_no from works_on where emp_no in (select emp_no from employee where dept_no in (select dept_no from department where dept_name='marketing'))

--15
select project_no, project_name into #project_temp from project
select * from #project_temp
CREATE TABLE #project_temp(project_no CHAR(4),
                        project_name CHAR(15),
                        budget FLOAT)
Temporary tables are  used to store intermediate calculations in a complex series of CREATE or UPDATE queries that produce some sort of analysis result. Temporary tables are also sometimes used to increase performance, in certain situations.