SQL queries doubts -asking for help again

Question

Hi all,
I have been trying to design a schema with all objects needed.Infact,i have completed with all tables and inserting data
in them.
But,am very confused and mixed with the RELATIONSHIP between tables because now when i have to retrieve data-then
writing proper query ..correct one is a complicated procedure.
I feel since i am very new to this,the design hasnt been effecient.
Scenario has a specific table with employees, departments, and projects.
employees
eid ename Salary               
1 Emp1 1000          
2 Emp2 100
3 Emp3 189
4 emp4 200
5 emp5 300
6 emp6 400
departments
**each department has one manager
DEPTid     NAME          LOCATION           mgrid     
10       ACCOUNTING       NEW YORK     0
20        RESEARCH       DALLAS          1
30        SALES       CHICAGO      2
40        OPERATIONS       BOSTON          3RELATIONSHIP Table for employee nd department and Manager ---->created seperate table as 1 :M relationships
(**one person can belong to multiple departments )
EMP_mngr_dept
E_ID     DEPt_ID     mgrid     
1     10     200
208     50     121
1     30     114
121     20     201
114     10     200**Projects table
There are many projects owned by different deparments.A project can belong to only 1 department.
PROJECT_NAME           PROJECT_STATs     PROJECT_ID     PROJECT_FROM_DT_TM     COST                   DEPARTMENT_ID
ACCOUNT_PRO          Active                1          2/17/1996          2000000                    10
MMC_PRO                          Active          2          2/20/2006          20000000                    20
STUDENT_MANAGEMENT     Active          3          2/25/2007          2000000          40***Relationship table employees and projects
A person can be in many projects at a time
EMP_project_Rltn
PROJECT_ID     EMPLOYEE_ID     START_DATE     END_DATE
1          1          
2          1          
1          208          
2          208          
5          10          2/21/2009 3:45:53 AM     (1)QUERY to MOVE A PERSON FROM ITS EXISTING DEPARTMENT TO ANOTHER DEPARTMENT.
Does this mean that even the PROJECT info for the person changes when he moves to another dept?What woulc be the query then?
(2)Show details of person, his managers , departments and project he works.
is the below join proper? Please advise me ....if i have used many extra tables for this.
select * from employees e, EMP_mngr_dept emd,departments d,EMP_project_Rltn p,
projects p1
where e.employee_id =1
and emd.employee_id = e.employee_id
and emd.department_id =d.department_id
and p.employee_id = e.employee_id
and p1.project_id = p.project_id
PLEASE PLEASE ADVISE AND HELP ME IF THE ABOVE TABLES CREATED ARE MUST NEEDED AND EFFICIENT FOR MY SCENARIO.i AM VERY CONFUSED WITH THE NO OF TABLES REQUIRED.
query to find expenditure of all projects together in terms of salary.
(3)SQL to be able to show a person--->manager-->and their manager's MANAGER
(4)How will managers to view all employees reporting to him.
Edited by: [email protected] on Feb 23, 2009 2:55 AM
Edited by: [email protected] on Feb 23, 2009 3:43 AM

Answer 1

Hi,
user_7000011 wrote:
(3)SQL to be able to show a person--->manager-->and their manager's MANAGER
select * from employees where employee_id in (
select manager_employee_id from emp_manager_dept where employee_id =****)
Start by showing a person and his managers. (Once you learn how to do this, adding the managers' managers will be easy.)
Pretend that the person is in one table (let's call this table p), and their managers are in another (let's call it m).
You can get all the information you need about the person using a query on table p.
You can find who that person's managers are (just their id's) by joining p to emp_mgr_dept.
You can find all the information about those managers by joining table m.
So this is a three-way join: no sub-queries are needed. All the join conditions are simple equi-joins, such as "p.eid = emd.e_id".
Since p and m are really the same table (employees), the FROM clause will contain two copies of employess, one with the alias p, the other aliased m.
Notice that the query invloves three tables, but you do not need to display any columns from one of them. This happens a lot.
(4)How will managers to view all employees reporting to him.
select * from employees where employee_id in
(select employee_id from emp_manager_dept where manager_employee_id in
(select employee_id from employees where first_name ='***'))
This is very similar to the problem above. I would solve this problem the same way, with a three-way join.The main difference is that you are starting with the manager's name, not the person's name. The relationships between the tables are the same.
Another minor difference is that you do not need to display any information from the m or emp_mgr_dept tables. This is a little more unusual, but not really different from, the problem above, wherre the SELECT clause referenced two tables out of three.
You could also use sub-query to solve this problem, but I don't recommend it.