I'm very new to universe design and would really appreciate a point in the right direction...
I have a table Sales that records details of sales made by staff members. It includes the following fields:
SaleID
StaffID
SaleDate
I also have a table StaffDepts that has the historic department information for each member of staff:
StaffID
DeptName
StartDate
EndDate
I would like to build a universe that pulls through the name of the department in which the member of staff was placed on the date of the sale.
I tried linking the two tables with three joins in Designer (I amended the Expression box in the Edit Join window of each join):
Sales.StaffID = StaffDepts.StaffID
StaffDepts.StartDate <= Sales.SaleDate
(StaffDepts.EndDate IS NULL) OR (StaffDepts.EndDate > Sales.SalesDate)
This failed pretty spectacularly! Can any suggest how I can achieve what I am trying to do?!
Many thanks!
You've created three separate joins in Designer, but I believe you really want them all to work as one. You can (and if I understand what you want to do here, should) create only one join in Designer and include all of the clauses above in it with AND.
I'm assuming the spectacular fail was because by creating three separate joins, you'd introduced loops into your universe. You would only want to create separate joins if you needed the two tables to be joined differently in different contexts -- and in that case, you would create those separate contexts and assign the joins to them accordingly.
Related
New to this...
I have a table QAQC_Studies that includes titles, dates, and subject matter
I have another table QAQC_Publications that includes citation information for multiple publications resulting from a single study in the first table.
Every 3 months I need to create a report to QC studies added by coworkers so I run the following query (with some additional attributes removed for brevity). The where clause is a list of study IDs they provide me (often 15-20 different studies).
SELECT QAQC_Studies.StudiesID,
QAQC_Studies.NSL,
QAQC_Studies.StudyTitle,
QAQC_Studies.Abstract,
QAQC_Studies.StudyStatus
FROM QAQC_Studies
WHERE [QAQC_Studies].[StudiesID]=26806 or 26845
I'd like to add to that report a list of the publications associated with each study.
How do I write the Where clause in the second query to reference those studies indicated in the first query?
You can use a subquery. Something like:
SELECT [QAQC_Publications].[QAQC_Field]
FROM [QAQC_Publications]
WHERE [QAQC_Publications].[StudiesID] --or whichever field the two tables
--share for publication/study connection
IN (SELECT QAQC_Studies.StudiesID
FROM QAQC_Studies
WHERE [QAQC_Studies].[StudiesID]=26806 or 26845)
I'm a college student and the database I'm working with is purely fictional but part of it requires me to make a query that is a join.
What I have are 3 tables each with part of the data but also needing to use two of those tables as conditions based off the main table. What I mean is I have an employee table, order table and customer table and the only thing any two of them have in common is the ID of either the employee or the customer is part of the order table.
Now what I am trying to do is create a join statement that will get certain information from the employee and customer tables and only those that both the employee and the customer are also on the same line in the order table. How should i make this type of conditional statement?
Any example using the same basic scenario will work I can use that to help me build my own query.
This is what I have right now:
SELECT [Customer/Vendor_Info_local].Name_of_customer,
Employee_Info_local.Employee_Name
FROM Employee_Info_local,
[Customer/Vendor_Info_local],
Order_Information_local
WHERE (([Customer/Vendor_Info_local].[Customer/VendorID] =
[Order_Information_local].[Cusrtomer/VendorID])
AND
([Employee_Info_local].[EmployeeID] = [Order_Information_local].[EmployeeID]));
I keep getting a type mismatch error when i try to use it and honestly not even sure what that means.
I've got a problem with an Asset Database that I have been developing for a customer in MSSQL. It entails capturing Required Actions, for example Lifting Equipment at a specific location needs to be inspected 6 months after purchase. The Due Dates for these required actions can be calculated in different ways but to simplify here will be calculated based on their Purchase Date.
So to that end I have a table called tblActionsRequired that contains the following relevant fields:
ActionID - for the action required
EquipmentCategoryID or EquipmentTypeID or EquipmentID - so either one of these fields are required. With this they specify that an action is required for either a category of equipment or an equipment type or a specific piece of equipment. So an example would be that a 2kg Powder Fire Hydrant would be an equipment type, it would fall into the category Fire Safety Equipment and there might be a specific 2kg Powder Fire Hydrant with an asset number of say PFH2KG001.
BasedAtID - the company's branches or sites
Ideally what I'd like to do is keep as much as possible in one query as opposed to creating separate queries or views for every combination and then adding them together using UNIONs. I have several other similar fields by which these required actions can be segmented so it may seem simple enough here to just use unions but I've calculated I would need to cater for 48 different combinations and probably create a View for each and then UNION them together!
So next I have tblEquipment that contains the following relevant keys:
EquipmentID - the primary key
EquipmentTypeID = foreign key, which Equipment Type this asset is a member of
BasedAtID - foreign key, which site the asset is located at
The Equipment Types then belong to Equipment Categories and the Categories then allow building a tree structure with parent-child relationships, but these I think I have sufficiently taken care of in creating a view called vwCategoryTree with the following fields:
ParentCategoryID
EquipmentTypeID
This view has been tested and checks out fine, it cuts through the tree structure and allows you to perform joins between EquipmentTypeID and their ultimate parents with EquipmentCategoryID.
What I need help with is how to do some sort of conditional join between tblActionsRequired and tblEquipment based on which of the fields EquipmentCategoryID, EquipmentTypeID, or EquipmentID have a value. If only EquipmentID or EquipmentTypeID could be specified then I think this would work:
ON (tblActionsRequired.EquipmentID IS NOT NULL AND tblEquipment.EquipmentID = tblActionsRequired.EquipmentID) OR (tblActionsRequired.EquipmentTypeID IS NOT NULL AND tblActionsRequired.EquipmentTypeID = tblEquipment.EquipmentTypeID)
But how do I bring a third table into this join to cater for EquipmentCategoryID or at least avoid having to use a UNION?
Sorry if something doesn't make sense, please just ask! Thank you very much!
One possible approach:
select ...
from tblEquipment e
left join vwCategoryTree c on e.EquipmentTypeID = c.EquipmentTypeID
join tblActionsRequired r
on (e.EquipmentID = r.EquipmentID or
e.EquipmentTypeID = r.EquipmentTypeID or
c.ParentCategoryID = r.EquipmentCategoryID)
I have two table Employee and Salary table, salary consists Salary of employee in a field named Salary_employee.
Second one is Extra Expense, Extra expense consists records related to extra expenses of a company like electricity bills,office maintenance in a field named extra_expense.
(Their is no relationship between these two table).
Finally, I just wanted to show all the expenses of company in a report, for this i need to group both the table. what to use here join or union ??.
If there is no relationship between the two tables, then this really cannot work since you dont know where the expense is supposed to tie into. You should redesign the database if possible as this sounds impossible based on your description.
UPDATE
OK, by the look of your screenshots, I am guessing that this database only stores one companies info? And not multiple?
IF that is correct, AND if all you want to do is squish the data together into one flowing report of expenses, then I would indeed suggest a UNION. A JOIN would not give you the flow you are looking for. A UNION will just smash the two outputs together into one...which I think is what you are asking for?
SELECT ext_amount AS amount, ext_date AS date_of_trans
FROM extra_expenses
UNION
SELECT sal_cash AS amount, sal_dateof_payment AS date_of_trans
FROM employee_salary
It sounds like you don't need to use group or join. Simply query both tables separately within a script and handle them both accordingly to their structure to produce a report.
Join and union are functions which you can use to extract different information on a common thing from separate tables. E.g. if you have a user whose private details are stored in one table, but their profile information is in another table. If you want to display both private details as well as profile info, you can join the two tables by the common user name in order to combine and gather all info on the user in one query.
When I have to select a number of fields from different tables:
do I always need to join tables?
which tables do I need to join?
which fields do I have to use for the join/s?
do the joins effects reflect on fields specified in select clause or on where conditions?
Thanks in advance.
Think about joins as a way of creating a new table (just for the purposes of running the query) with data from several different sources. Absent a specific example to work with, let's imagine we have a database of cars which includes these two tables:
CREATE TABLE car (plate_number CHAR(8),
state_code CHAR(2),
make VARCHAR(128),
model VARCHAR(128),);
CREATE TABLE state (state_code CHAR(2),
state_name VARCHAR(128));
If you wanted, say, to get a list of the license plates of all the Hondas in the database, that information is already contained in the car table. You can simply SELECT * FROM car WHERE make='Honda';
Similarly, if you wanted a list of all the states beginning with "A" you can SELECT * FROM state WHERE state_name LIKE 'A%';
In either case, since you already have a table with the information you want, there's no need for a join.
You may even want a list of cars with Colorado plates, but if you already know that "CO" is the state code for Colorado you can SELECT * FROM car WHERE state_code='CO'; Once again, the information you need is all in one place, so there is no need for a join.
But suppose you want a list of Hondas including the name of the state where they're registered. That information is not already contained within a table in your database. You will need to "create" one via a join:
car INNER JOIN state ON (car.state_code = state.state_code)
Note that I've said absolutely nothing about what we're SELECTing. That's a separate question entirely. We also haven't applied a WHERE clause limiting what rows are included in the results. That too is a separate question. The only thing we're addressing with the join is getting data from two tables together. We now, in effect, have a new table called car INNER JOIN state with each row from car joined to each row in state that has the same state_code.
Now, from this new "table" we can apply some conditions and select some specific fields:
SELECT plate_number, make, model, state_name
FROM car
INNER JOIN state ON (car.state_code = state.state_code)
WHERE make = 'Honda'
So, to answer your questions more directly, do you always need to join tables? Yes, if you intend to select data from both of them. You cannot select fields from car that are not in the car table. You must first join in the other tables you need.
Which tables do you need to join? Whichever tables contain the data you're interested in querying.
Which fields do you have to use? Whichever fields are relevant. In this case, the relationship between cars and states is through the state_code field in both table. I could just as easily have written
car INNER JOIN state ON (state.state_code = car.plate_number)
This would, for each car, show any states whose abbreviations happen to match the car's license plate number. This is, of course, nonsensical and likely to find no results, but as far as your database is concerned it's perfectly valid. Only you know that state_code is what's relevant.
And does the join affect SELECTed fields or WHERE conditions? Not really. You can still select whatever fields you want and you can still limit the results to whichever rows you want. There are two caveats.
First, if you have the same column name in both tables (e.g., state_code) you cannot select it without clarifying which table you want it from. In this case I might write SELECT car.state_code ...
Second, when you're using an INNER JOIN (or on many database engines just a JOIN), only rows where your join conditions are met will be returned. So in my nonsensical example of looking for a state code that matches a car's license plate, there probably won't be any states that match. No rows will be returned. So while you can still use the WHERE clause however you'd like, if you have an INNER JOIN your results may already be limited by that condition.
Very broad question, i would suggest doing some reading on it first but in summary:
1. joins can make life much easier and queries faster, in a nut shell try to
2. the ones with the data you are looking for
3. a field that is in both tables and generally is unique in at least one
4. yes, essentially you are createing one larger table with joins. if there are two fields with the same name, you will need to reference them by table name.columnname
do I always need to join tables?
No - you could perform multiple selects if you wished
which tables do I need to join?
Any that you want the data from (and need to be related to each other)
which fields do I have to use for the
join/s?
Any that are the same in any tables within the join (usually primary key)
do the joins effects reflect on fields specified in select clause or on where conditions?
No, however outerjoins can cause problems
(1) what else but tables would you want to join in mySQL?
(2) those from which you want to correlate and retrieve fields (=data)
(3) best use indexed fields (unique identifiers) to join as this is fast. e.g. join
retrieve user-email and all the users comments in a 2 table db
(with tables: tableA=user_settings, tableB=comments) and both having the column uid to indetify the user by
select * from user_settings as uset join comments as c on uset.uid = c.uid where uset.email = "test#stackoverflow.com";
(4) both...