I am trying to display employee properties using C# WPF view.
I have data in '2' different oracle tables in my database:
Those tables structure at high-level is...
Employee table (EMP) - columns:
ID, Name, Organisation
Employee properties table (EMPPR) - columns
ID, PropertyName, PropertyValue
The user will input 'List of Employee Name' and I need to display Employee properties using data in those '2' tables.
Each employee has properties from 40-80 i.e. 40-80 rows per employee in EMPPR table. In this case, which approach is more efficient?
Approach #1 - single query data retrieval:
SELECT Pr.PropertyName, Pr.PropertyValue
FROM EMP Emp, EMPPR Pr
WHERE Emp.ID = Pr.ID
AND Emp.Name IN (<List of Names entered>)
Approach #2 - get IDs list using one query and Get properties using that ID in the second query
Query #1:
SELECT ID
FROM EMP
WHERE Name IN (<List of Names entered>)
Query #2:
SELECT PropertyName, PropertyValue
FROM EMPPR
WHERE ID IN (<List of IDs got from Query#1>)
I need to retrieve ~10K employee details at once where each employee has 40-80 properties.
Which approach is good?
Which query is faster?
The first one, which uses a single query to fetch your results.
Why? much of the elapsed time handling queries, especially ones with modestly sized rows like yours, is consumed going back and forth from the client to the database server.
Plus, the construct WHERE something IN (val, val, val, val ... ... val) can throw an error when you have too many values. So the first query is more robust.
Pro tip: Come on into the 21st century and use the new JOIN syntax.
SELECT Pr.PropertyName, Pr.PropertyValue
FROM EMP Emp
JOIN EMPPR Pr ON Emp.ID = Pr.ID
WHERE Emp.Name IN (<List of Names Inputted>)
Use first approach of join between two tables which is far better than using where clause two times.
Related
I have two different tables with records I need to join together in a way I can't quite figure out how to make work. My data looks like this.
Table A
Columns: Employee_ID, Employee_Department, Employee_Team, Manager_ID, Is_a_Manager ... many other columns
Sample Values:
12345 Department1 Team1 67890 Yes/No
.
.
.
One employee per row, several thousand rows comprising the entire company
Table B
Employee_ID, Manager_ID ... other columns
The exact same data set as Table A
Currently I'm combining those two tables (and three others) with a simple join on Employee_ID, which I'm then using as a data source in Tableau to visualize the data.
What I'd like to do with a SQL script is as follows:
Check to see whether an employee in Table A is a manager or not based on the Is_a_Manager column
If they are, find an employee in Table B who is one of their direct reports by matching the employee ID in Table A to the Manager ID in Table B.
Lookup that direct report's department and team in Table A by matching the Employee_ID in Table B to Employee_ID in Table A and displaying the Employee_Department and Employee_Team columns.
Add the direct report's department and team to two new columns in the original manager's Table A row
I'd like the final output in Table A to be something like
Employee_ID, Employee_Department, Employee_Team, Manager_ID, Is_a_Manager? ... Direct_Report_Department, Direct_Report_Team
Also, an important point is that some managers will have employees who are on different teams, so values in the Direct_Report_Department and Direct_Report_Team are not distinct. I only actually need any one employee's Department and Team to display, it doesn't matter which employee's it is.
Finally, I am able to do step 1 fairly easily in Tableau, so if the SQL script could do steps 2-4 and simply return a null value if the employee was not a manager, that would work for me as well.
Any ideas on how to accomplish this would be greatly appreciated. Thank you!
This should work based on the requirement provided. You don’t have to do any of the steps in Tableau and can simply export the output from the SQL as your data source
Select Tb1.Employee_ID, Tb1.Employee_Department, Tb1.Employee_Team, Tb1.Manager_ID, Tb1.Is_a_Manager, Tb3. Direct_Report_Department, Tb3. Direct_Report_Team
from Table_A Tb1
join (Select Manager_id, max(Employee_id) as emp_id from Table_B group by Manager_id) Tb2
on Tb1.Employee_id = Tb2.Manager_id
left join (Select Employee_ID, Employee_Department as Direct_Report_Department, Employee_Team as Direct_Report_Team from Table_A group by Employee_ID, Employee_Department, Employee_Team) Tb3
on Tb2.emp_id = Tb3.Employee_ID
where Tb1.Is_a_Manager = 'Yes';
I am still learning the ropes of SQL so I have run into my first obstacle. I am to create an SQL query that retrieves employee.firstname, employee.lastname, dependents.depname, and dependents.birthday from the two tables employees and dependents.
I am only supposed to show an employee if he or she has a dependent.
My primary table (employee; only the first 43 rows): employee table
My secondary table (dependents): dependents table
This is what I have so far:
SELECT
employee.firstname, employee.lastname,
dependents.depname, dependents.birthday
FROM
employee
INNER JOIN
dependents ON employee.id = dependents.empid
This works fine however I run into many duplicate rows of data:
Original Query
This is not the full query result but I think it provides sufficient evidence of my problem.
I used the DISTINCT keyword with my SELECT statement, but it only retrieved a small number of my dependents.
Adding DISTINCT
Have you already any duplicates in one of the tables employee or dependents? The second result looks correct. With select distinct the database removes all duplicates from the result set.
I need to match up an employee with a task in a small Microsoft Access DB I built. Essentially, I have a list of 45 potential tasks, and I have 25 employees. What I need is:
Each employee to have at LEAST one task
No employee to have more than TWO
Be able to randomize the results every time I run the query (so the same people don't get consistently the same tasks)
My table structure is:
Employees - w/ fields: ID, Name
Tasks - w/ fields: ID, Location, Task Group, Task
I know this is a dumb question, but I truly am struggling. I have searched through SO and Google for help but have been unsuccessful.
I don't have a way to link together employees to tasks since each employee is capable of every task, so I was going to:
1. SELECT * from Employees
2. SELECT * from Tasks
3. Union
4. COUNT(Name) <= 2
But I don't know how to randomize those results so that folks are randomly matched up, with each person at least once and nobody more than twice.
Any help or guidance is appreciated. Thank you.
Consider a cross join with an aggregate query that randomizes the choice set. Currently, at 45 X 25 this yields a cartesian product of 1,125 records which is manageable.
Select query (save as a query object, assumes Tasks has autonumber field)
SELECT cj.[Emp_Name], Max(cj.ID) As M_ID, Max(cj.Task) As M_Task
FROM
(SELECT e.[Emp_Name], t.ID, t.Task
FROM Employees e,
Tasks t) cj
GROUP BY cj.[Emp_Name], Rnd(cj.ID)
ORDER BY cj.[Emp_Name], Rnd(cj.ID)
However, the challenge here is this above query randomizes the order of all 45 tasks per each of the 25 employees whereas you need the top two tasks per employee. Unfortunately, MS Access does not have a row id like other DBMS to use to select top 2 per employee. And we cannot use a correlated subquery on Task ID per Employee since this will always return the highest two task IDs by their value and not random top two IDs.
Therefore to do so in Access, you will need a temp table regularly cleaned out prior to each allocation of employee tasks and use autonumber for selection via correlated subquery.
Create table (run once, autonumber field required)
CREATE TABLE CrossJoinRandomPicks (
ID AUTOINCREMENT PRIMARY KEY,
Emp_Name TEXT(255),
M_ID LONG,
M_Task TEXT(255)
)
Delete query (run regularly)
DELETE FROM CrossJoinRandomPicks;
Append query (run regularly)
INSERT INTO CrossJoinRandomPicks ([Emp_Name], [M_ID], [M_Task])
SELECT [Emp_Name], [M_ID], [M_Task]
FROM mySavedCrossJoinQuery;
Final query (selects top two random tasks for each employee)
SELECT c.name, c.M_Letter
FROM CrossJoinRandomPicks c
WHERE
(SELECT Count(*) FROM CrossJoinRandomPicks sub
WHERE sub.name = c.name
AND sub.ID <= c.ID) <= 2;
I have two tables in a Database
and
I need to retrieve the number of staff per manager in the following format
I've been trying to adapt an answer to another question
SELECT bankNo AS "Bank Number",
COUNT (*) AS "Total Branches"
FROM BankBranch
GROUP BY bankNo
As
SELECT COUNT (*) AS StaffCount ,
Employee.Name AS Name
FROM Employee, Stafflink
GROUP BY Name
As I look at the Group BY I'm thinking I should be grouping by The ManID in the Stafflink Table.
My output with this query looks like this
So it is counting correctly but as you can see it's far off the output I need to get.
Any advice would be appreciated.
You need to join the Employee and Stafflink tables. It appears that your FROM clause should look like this:
FROM Employee INNER JOIN StaffLink ON Employee.ID = StaffLink.ManID
You have to join the Eployee table twice to get the summary of employees under manager
select count(*) as StaffCount,Manager.Name
from Employee join Stafflink on employee.Id = StaffLink.EmpId
join Employee as Manager on StaffLink.ManId = Manager.Id
Group by Manager.Name
The answers that advise you on how to join are correct, assuming that you want to learn how to use SQL in MS Access. But there is a way to accomplish the same thing using the ACCESS GUI for designing queries, and this involves a shorter learning curve than learning SQL.
The key to using the GUI when more than one table is involved is to realize that you have to define the relationships between tables in the relationship manager. Once you do that, designing the query you are after is a piece of cake, just point and click.
The tricky thing in your case is that there are two relationships between the two tables. One relationship links EmpId to ID and the other links ManId to ID.
If, however, you want to learn SQL, then this shortcut will be a digression.
If you don't specify a join between the tables, a so called Cartesian product will be built, i.e., each record from one table will be paired with every record from the other table. If you have 7 records in one table and 10 in the other you will get 70 pairs (i.e. rows) before grouping. This explains why you are getting a count of 7 per manager name.
Besides joining the tables, I would suggest you to group on the manager id instead of the manager name. The manager id is known to be unique per manager, but not the name. This then requires you to either group on the name in addition, because the name is in the select list or to apply an aggregate function on the name. Each additional grouping slows down the query; therefore I prefer the aggregate function.
SELECT
COUNT(*) AS StaffCount,
FIRST(Manager.Name) AS ManagerName
FROM
Stafflink
INNER JOIN Employee AS Manager
ON StaffLink.ManId = Manager.Id
GROUP BY
StaffLink.ManId
I don't know if it makes a performance difference, but I prefer to group on StaffLink.ManId than on Employee.Id, since StaffLink is the main table here and Employee is just used as lookup table in this query.
I am new to SQL server, thus looking for some quick help on writing stored procedure:
brief about what I am doing:
employee says he is expert (type) in different domains (industries) and willing to work in countries of choice (mycountries) and my sal (minsal)and my native country (orgcountry)
Employer says he need so and so expert in the his choice of domain (industries) in the countries where openings are there and with sal range.
employee table has lots of records with columns like this:
name, email, myindustries, mycountries, mytype,minsal
employer table has lots of records with columns like:
expertneed, inindustries, incountries, sal-from, sal-to
now when employee logs in, he/she should get all the records of matching employers
when employer logs in, he/she also get all the records of matching employees.
can some one help in writing sp for this? appreciate any help
If you're storing comma-separated ids then you'll need a function to split a string into multiple rows. This is how you would use it:
SELECT DISTINCT employee.name [employee], employer.name [employer]
FROM employee
OUTER APPLY dbo.split(employee.myindustries) myi (industry)
OUTER APPLY dbo.split(employee.mycountries) myc (country)
JOIN employer
OUTER APPLY dbo.split(employer.inindustries) ini (industry)
OUTER APPLY dbo.split(employer.incountries) inc (country)
WHERE employer.expertneed = employee.type
AND ini.inindustries = myi.industry
AND inc.incountries = myc.country
AND employee.minsal BETWEEN employer.[sal-from] AND employer.[sal-to]