I have two tables:
1) employee with columns: e_id, e_name, address;
2) project with columns: p_id, p_name, start_Date, End_Date.
There is a many-to-many relationship between these two tables.
How can I store this relationship and how can I query for retrieving "Employee details and project details on which he is working"?
You need a cross reference table inbetween:
EmployeeProjectXref: e_id, p_id
The combination of e_id and p_id can be the primary key for this Xref table.
Then, if #e_id is a variable holding the selected Employee ID:
SELECT E.e_name, P.p_name
FROM EmployeeProjectXref EPX
JOIN Employee E ON E.e_id = EPX.e_id
JOIN Project P ON P.p_id = EPX.p_id
WHERE EPX.e_id = #e_id
ORDER BY P.Name
For more details, add them to the SELECT list. E.g.: SELECT E.e_name, E.address, P.p_name, P.start_date, P.end_date, etc. Here the E is an alias for the Employee table, and P is an alias for the Project table. This query will return one row for each entry in the EmployeeProjectXref table (provided that it references real entries in the Employee and Project tables.) If there is one employee and three projects, you'll get three rows.
Related
Suppose I have two tables:
Table 1: tasks with columns (id, authorId, assigneeId)
Table 2: employee with columns (id, name)
authorId and assigneeId in Table 1 are referenced to the id column in Table 2.
What is the way to select Task ID, Author Name and Assignee Name (Assignee name defaults to 'null' if no assigneeId is present) from these two tables?
I am not sure how to start, thus making it difficult. Could anyone give a hint on how to start the code?
You can join twice:
select t.id, e1.name as author_name, e2.name as assignee_name
from tasks t
left join employees e1 on e1.id = t.author_id
left join employees e2 on e2.id = t.assignee_id
I have the following tables
Lead
id varchar
employee_id varchar
Employee
id varchar
lead_id varchar
There will be a group of employees assigned to a lead. The Lead table holds the employee id of the lead.
The employee table will have lead_id which will be the id key of the leader.
The table will also contain employees which are not assigned to any lead
I need a query which will display the hierarchical result which will list the leaders and the employees under the leader
leader1 (employee )
employee1
employee 2
Leader 2(employee)
employee 3
employee 4
Any idea how this kind of hierarchical result can be obtained by a db2 query?
Click on the this link to view the table structure
The answer is a join of the two tables like
SELECT l.employee_id as leader_employee_id, e.id as employee_id
FROM LEAD l
INNER JOIN EMPLOYEE e
ON e.lead_id = l.employee_id
I need to display two columns from my attendance table (MEMBER_ID & MEETING_ID) and one column from my meeting table and finally two columns from my member table which displays the names that match with MEETING_ID.
The attendance table has a composite key (MEMBER_ID*, MEETING_ID*)
The member table's primary key is MEMBER_ID
Meeting table's primary key is MEETING_ID
My attempt is not working, can someone please help?
SELECT MEMBER_ID, MEETING_ID, MEETING_NAME MEMBER_FIRSTNAME, MEMBER_LASTNAME
FROM ATTENDANCE, MEMBER, MEETING
WHERE MEETING.MEMBER_ID = MEETING.MEMBER_ID;
End result needs to be:
MEMBER_ID MEETING_ID MEETING_NAME FIRSTNAME LASTNAME
0001 MEET0004 SPORTS DAY JOHN SMITH
May be you need this.
SELECT A.MEMBER_ID, A.MEETING_ID, M2.MEETING_NAME, M1.MEMBER_FIRSTNAME, M1.MEMBER_LASTNAME
FROM ATTENDANCE A, MEMBER M1, MEETING M2
WHERE M1.MEMBER_ID = A.MEMBER_ID
AND A.MEETING_ID = M2.MEETING_ID;
SELECT
a.MEMBER_ID
,a.MEETING_ID
,mt.MEETING_NAME
,mb.MEMBER_FIRSTNAME
,mb.MEMBER_LASTNAME
FROM
ATTENDANCE a
INNER JOIN MEMBER mb
ON a.MEMBER_ID = mb.MEMBER_ID
INNER JOIN MEETING mt
ON a.MEETING_ID = mt.MEETING_ID
;
Use Explicit Join Syntax and then setup your relationships using the ON conditions and the keys between the tables. Note I also used table aliases to shorten typying.
I have one table which contained 4 records (PersonName, CityName, CityState, CityCountry) in two different tables. One of the tables now has personID, personName and the other one has Cityid, CityName, CityState, CityCountry.
Now I created third table which hold PersonId, CityId. How can I populate that table with the ids of person and city from the original table since they are split now. I want to get the ids from the newly created tables based on the relationship they had in the original table.
Can you not just join back to the original table?
INSERT PersonCity (PersonID, CityID)
SELECT p.PersonID, c.CityID
FROM OriginalTable o
INNER JOIN Person p
ON p.PersonName = o.Personname
INNER JOIN City c
ON c.CityName = o.CityName
AND c.CityState = o.CityState
AND c.CityCountry = o.CityCountry;
My table has columns of data that contain employee keys for different departments. One column, for example would be business office, another admin.
I can't figure out how to write and sql that will join the employee master to return each persons name for each row. I could do it if it only had one column of employee master keys but it beat me
I think from what you have described you need to join to the Employee Master table multiple times:
SELECT A.Col1
, A.BOEmpID
, BO.EmpName
, A.AdminEmpID
, AD.EmpName
, <....>
FROM MyTable A
INNER JOIN Employees BO
ON A.BOEmpID = BO.EmpID
INNER JOIN Employees AD
ON A.AdminEmpID = AD.EmpID