I have two databases.
Table 1 (Student) has fields StudentID, EmployeeClass, StudentName. Here, EmployeeClass is varchar(5).
Table 2 (Employee) has fields EmployeeID, EmployeeName, Description, and EmployeeClass. Employee Class is nvarchar(5).
when i am writing Select Query as:
SELECT S.StudentID,
S.EmployeeClass,
S.StudentName
FROM Student AS S
LEFT OUTER JOIN Employee AS E
ON CAST(S.EmployeeClass AS VARCHAR(5)) = E.EmployeeID
WHERE E.Description = 'ABC'
All the values From employee table are showing as NULL? How to fix it
I think the join condition is wrong in your script.column 'EmployeeClass' refers to 'EmployeeID' in your script.
SELECT S.StudentID,
S.EmployeeClass,
S.StudentName
FROM Student AS S
LEFT JOIN Employee AS E
ON cast(S.EmployeeClass as varchar(5))= E.EmployeeClass
AND E.Description = 'ABC'
Related
Using SQL, my job is to fetch the SSN of students who enrolled in a course without enrolling in that course’s prerequisite(s). I'm using Access. The tables I need are as follows:
STUDENT (SSN, SNAME, MAJOR, DOB, ADDRESS)
ENROLLED (SSN, CID, GRADE)
PREQ (CID, PREQCID, PASSINGGRADE, NOTE)
Here's what I've done so far.
select *
from
(select SSN, CID from ENROLLED) AS enrolled
left join
(select CID, PREQCID FROM PREQ) AS prereq ON enrolled.CID = prereq.CID;
What I'm missing is how to check each row of the same student on the condition WHERE enrolled.CID = prereq.CID for a PREQCID that's NOT in enrolled.CID.
Is what I'm asking for here a loop? Am I on the right track? Please keep in mind this I'm in an introductory course so the simplest of solutions is preferable.
Here's another way using not exists:
select e1.ssn
from enrolled e1 left join preq p on e1.cid = p.cid
where
p.preqcid is not null and
not exists (select 1 from enrolled e2 where e2.ssn = e1.ssn and e2.cid = p.preqcid)
This is essentially stating:
"Select the ssn for all enrollments where there is a prerequisite course and the prerequisite course ID does not exist in the table of enrollments for that ssn."
I use select 1 purely for optimisation - we don't care about the values held by the nested query, only whether or not the nested query returns one or more records.
You could also write this using joins as:
select e1.ssn
from
(
enrolled e1 left join preq p on e1.cid = p.cid
)
left join enrolled e2 on
p.preqcid = e2.cid and e1.ssn = e2.ssn
where
e2.cid is null
Here, the enrolled table is referenced twice: the first is left joined on the table of prerequisite courses for each course, and the second is left joined on the prerequisite course ID and the ssn from the original enrollment.
The where clause then causes records to be selected for which the link on the prerequisite course is null for the given ssn.
I'm sure there is a cleaner way to do this, but this gets you your result:
Select S.SSN, E.CID From Student S
Inner Join Enrolled E on E.SSN = S.SSN
Where E.CID IN (Select CID From PREQ Where Preqcid NOT IN
(Select CID From Enbrolled Where SSN = S.SSN))
This might work if analytic functions and CTEs are available:
with d as (
select ssn, cid,
count(distinct p.cid) over (partition by e.ssn, e.cid) ecnt, ,
count(distinct e.cid) over (partition by e.ssn, p.cid) pcnt
from enrolled e left outer join preq p on p.cid = e.cid
)
select distinct ssn, cid from d
where ecnt = pcnt;
I want to get the number of employees by department and I wrote this script using Oracle but it always says that there is a missing expression
The columns used in my tables :
department :name (the name of the department) -
depnum (the id of the department"primary key"),
employee : empnum (the id of the employee) -
depnum (the id of the department in which the employee in question is working "foreign key")
Query:
select
s.name
from
department s
inner join
employee p on s.depnum = p.depnum
group by
s.name
having
count(p.empnum) = max(select count(p.empnum)
from employee p, department s
where s.depnum = p.depnum
group by s.name) ;
If you want the number of employees by department, I would expect something like this:
select s.name, count(*) as num_employees
from department s inner join
employe p
on s.depnum = p.depnum
group by s.name ;
If you want the department names with the maximum number of names, you can use a having clause:
select s.name, count(*) as num_employees
from department s inner join
employe p
on s.depnum = p.depnum
group by s.name
having count(*) = (select max(cnt)
from (select count(*) as cnt
from employee e2
group by e2.depnum
) e2
);
The problem with your query is that you are attempting to take the max() of a subquery. That syntax is not allowed -- and not necessary.
you sql statement is not correct that's why it thrown that error. I think you tried something like below
select s.name
from department s
inner join employe p on s.depnum=p.depnum
group by s.name
having count(p.empnum)=
select max(cnt) from
(
select count(p.empnum) as cnt
from employe p join department s
on s.depnum=p.depnum
group by s.name
) t;
Can you please help me, I don't know how to create this query. I am a front end dev.
Expected result should be table with 2 columns
Name(one) DepartmentName(many)
The tables and their relationship are shown in this image:
You can do this with a couple of INNER JOINS. You don't need to reference the Location table in this query because Employee.LocationId is the same as EmployeeDepartment.LocationId.
This simple query will return all employee names and all department names they are related to. The employee name may be repeated, as this query puts only one department name in the column, so if an employee is in two departments, you get the employee name twice.
SELECT
EmployeeName = e.Name
,DepartmentName = d.Name
FROM Employee e
INNER JOIN EmployeeDepartment ed ON ed.LocationId = e.LocationId
INNER JOIN Department d ON d.id = ed.DepartmentId
This query is a bit more complicated, but returns each employee name only once, and the department names will be a comma-separated string of names. This is accomplished by using STUFF() in conjunction with FOR XML.
;WITH EmployeesAndDepartments AS
(
SELECT
EmployeeName = e.Name
,DepartmentName = d.Name
FROM Employee e
INNER JOIN EmployeeDepartment ed ON ed.LocationId = e.LocationId
INNER JOIN Department d ON d.id = ed.DepartmentId
)
SELECT
ead.EmployeeName
,Departments = STUFF((
SELECT ',' + DepartmentName
FROM EmployeesAndDepartments
FOR XML PATH('')
) , 1, 1, ''
)
FROM EmployeesAndDepartments ead
GROUP BY ead.EmployeeName
This should work
SELECT
e.Name
, d.Name AS DepartmentName
FROM
Employee e
LEFT OUTER JOIN
EmployeeDepartment ed
ON e.LocationId = ed.LocationId
LEFT OUTER JOIN
Department d
ON ed.DepartmentId = d.id
Note that the use of LEFT OUTER JOIN will return the employee even if they don't have a corresponding record in EmployeeDeparatment and/or Department. If you only want to retrieve employees that do have corresponding EmployeeDepartment and Department records, use INNER JOIN instead
I have an EmployeeDepartmetn juction table like this. I have all the departments in Depeartment table and employees in Employee table..
I want to get departments for an particular employee along with the all the departments available in depeartment table.
It should be like Select DepartmentId, DepartmentName, EmployeeID from Query.
Main criteria here is, Need to display NULL if the employee dont have that department. I am confused here...please help.
Please give Linq Query
Thanks in Advance
Put criteria in your left join:
Select distinct a.DeptID, b.DepartmentName, b.EmployeeID
From Department a
left join EmployeeDepartment b
on a.DeptID = b.DeptID and b.EmployeeID = 1 --insert employee ID here
It will show all departments (even those with no employees), then show the employee ID you chose in the third column only if that employee is assigned there.
You can do this with conditional aggregation:
select DeptId,
max(case when EmployeeId = 1 then EmployeeId end) as EmployeeId
from EmployeeDepartment ed
group by DeptId;
EDIT:
If you have a departments table as well:
select d.deptid, d.name, ed.employeeid
from Departments d left join
EmployeeDepartment ed
on d.deptid = ed.deptid and
ed.employeeid = 1;
I have 2 tables,
The first one is called emp, and has 2 columns called id and name
The second one is called dep, and has columns called id and empid and nameOfDep
if I want to list all emp that have X dep, but don't have Y dep
This is an example I use
Select e.id, e.name
from emp e
where e.id in (Select empid from deptid where deptid=X)
and e.id not in (Select empid from deptid where deptid=Y);
How I can make it using JOIN instead of with subqueries?
An IN can be converted into an INNER JOIN. A Not IN can be converted to LEFT JOIN / NULL Test. Sometimes called an ANTI JOIN.
SELECT e.id,
e.name
FROM emp e
INNER JOIN deptid D_X
ON e.empid = d_x.empid
AND deptid = 'X'
LEFT JOIN deptid D_Y
ON e.empid = d_Y.empid
AND deptid = 'Y'
WHERE d_Y.empid IS NULL
Also I'm making the assumption that when you wrote deptid = X that you meant X to be a literal string and not a field name
SELECT e.id, e.name
FROM emp e
INNER JOIN dep d ON (e.deptID = d.deptID AND d.deptID NOT y)
Add the Department ID to the employee record and then join on that.
EDIT
My bad, updated.
EDIT
Helps to read, go with Conrad's answer.