I want to report from a selection on multiple tables with filters to apply.
Nothing new, but I'm wondering what is the best possible implementation (considering I'm using an S/4HANA system).
Specification
Data
For example, we want to retrieve the data from the tables:
EKKO order header
EKPO order item
EKKN order item assignment
EKBE order item historic
Tables have the following relationships :
EKKO 1 - n EKPO
EKPO 1 - n EKKN
EKPO 1 - n EKBE
Filters
We would like at least one element of each table to be present (INNER JOIN), if the header does not have an item we do not upload the header data, if the item has no allocation we do not upload the data of the post, etc.
We would apply filters to several table areas, for example
EKPO-WERKS plant
etc...
Implementation
Select with join
The first solution would be to make a selection on all the tables with joins and then disassemble them after with LOOP AT ... GROUP BY... then LOOP AT GROUP.
But already there I'm asking myself questions !
In what order should the data be selected ? EKKO->EKPO->etc. or EKPO->EKKO etc.
Multiple Select
Select headers then the items according to the headers then the assignment according to the items etc.
The advantage is that it is more readable (not sure) and we have less redundant data, on the other hand we must apply certain filters
post selection in ABAP.
???
Another solution ?
Conclusion
So I'm a little lost and I would like to have your opinion.
Related
I have two data sources that are loaded into Azure Synapse. Both raw data sources contain an 'Apple' table.
I merge these into a single 'Apple' table in my Enriched data store.
SELECT * FROM datasource1.apple JOIN datasource2.apple on datasource1.apple.id = datasource2.apple.id
However, both data sourecs also contain a one to many relation AppleColours.
Please could someone help me understand the correct approach to creating a single AppleColours table in my enriched zone?
You need data from both sources when you want to merge them. JOIN(INNER JOIN) will bring only the apple.id that is in both datasource1 and datasource2.
You should try a CROSS JOIN
For the AppleColours 1 to many relation there are 2 methods:
You could put direct the color in the Apple table in this case there is no need for a separate AppleColours table
Apple
ID| Color
1 | red
2 | green
To get data into Color column make another JOIN this time with the AppleColours on the colorID from Apple table and AppleColours
Create a separate table AppleColours with ID and color. IN this table import both AppleColours tables from both datasources using a CROSS JOIN
Add a column in Apple table named AppleColorId which has the id's from AppleColours
If you want an Applet table that has all the data and don't need any join's to determine the apple color use method 1.
If you want a 'slim' apple table which has minimal data inside use method 2.
In this case to get the apple color you have to make an extra JOIN(INNER JOIN) to the AppleColour table
Maybe including a subquery making an UNION (you will get only one of each), but your problem still will be that, as each table has its own relationship with colours and you are joining both, same item can give you two different colours. My proposal: to make a switch to choose only one, If first is null, choose second, and if second is also null, a default value (some colour code). Other options are to use the lower id, because it was early created, or higher because it was the last...
Something like that
SELECT datasource1.*, datasource2.*, Q.Name, Q.Value FROM datasource1.apple
JOIN datasource2.apple on datasource1.apple.id = datasource2.apple.id
JOIN
(SELECT ColourID, Name, Value FROM datasource1.AppleColours UNION SELECT ColourID, Name, Value FROM datasource2.AppleColours) Q
ON Q.ColourID = COALESCE(datasource1.ColourID, datasource2.ColourID, {DefaultColor})
Are the two data sources supposed to represent slices of the same real population?
I.e., if full joining datasource1 with datasource2 on apple.id is logically consistent, then full joining AppleColours between the 2 datasources should be logically correct as well.
The one-to-many then logically preserves the information from the two datasets, and remains correctly one-to-many. If there are any relationships cardinality violations as the results of this join - those weren't the right cardinalities to begin with.
(btw, should be a full join)
I have the following problem.
I have a table Entries that contains 2 columns:
EntryID - unique identifier
Name - some name
I have another EntriesMapping table (many to many mapping table) that contains 2 columns :
EntryID that refers to the EntryID of the Entries table
PartID that refers to a PartID in a seprate Parts table.
I need to write a SP that will return all data from Entries table, but for each row in the Entries table I want to provide a list of all PartID's that are registered in the EntriesMapping table.
My question is how do I best approach the deisgn of the solution to this, given that the results of the SP would regularly be processed by an app so performance is quite important.
1.
Do I write a SP that will select multiple rows per entry - where if there are more than one PartID's registered for a given entry - I will return multiple rows each having the same EntryID and Name but different PartID's
OR
2.
Do I write a SP that will select 1 row per entry in the Entries table, and have a field that is a string/xml/json that contains all the different PartID's.
OR
3. There is some other solution that I am not thinking of?
Solution 1 seems to me to be the better way to go, but I will be passing lots of repeating data.
Solution 2 wont pass extra data, but the string/json/xml would need to be processed additionally, resuling in larger cpu time per item.
PS: I feel like this is quite a common problem to solve, but I was unable to find any resource that can provide common solutions or some pros/cons to different approaches.
I think you need simple JOIN:
SELECT e.EntryId, e.Name, em.PartId
FROM Entries e
JOIN EntriesMapping em ON e.EntryId = em.EntryId
This will return what you want, no need for stored procedure for that.
I am trying to calculate hours flowing in and out of a cost center. When the cost center lends out an employee for an hour it's +1 and when they borrow an employee for an hour it's -1.
Right now I'm using a query that says
select
columns
from dbo.table
where EmployeeCostCenter <> ProjectCostCenter
So when ProjectCostCenter = ID_CostCenter it returns +HoursQuantity.
Then I update ID_CostCenter = EmployeeCostCenter then where ID_CostCenter = EmployeeCostCenter to take -HoursQuantity.
That works fine. The problem is when I import it to Spotfire I can't filter on the main table even after I added the table relations. Can anyone explain why?
I can upload the actual code if needed, but I use 4 queries and a couple of them are quite lengthy. The main table, a temp table to calculate incoming hours, and a temp table to calculate outgoing hours are the only ones involved in this problem I think.
(moved to answer to avoid lengthy discussion)
Essentially, data relations are used to populate filtering / marking between different data-sets. Just like in RDBMS, the relation is what Spotfire uses as the link between dataset. Essentially it's the same as the column or columns you join on. Thus, any column that you wish to filter in TableA and have the result set limited in TableB (or visa versa) must be a relation.
Column matches aren't related columns, but are associated for aggregations, category axis, etc within each visualization. So if TableA has "amount" and TableB has "amount debit" and you wanted to use both of these in an expression, say Sum([TableA].[amount],[TableB].[amount debit]), they would need to be matched in order to not produce erroneous results.
Lastly, once you set up your relations, you should check your filter panel to set up how you want the filtering to work. You can have the rows included, excluded, or ignored all together. Here is a link explaining that.
Simplified situation:
I have a table, let's call it header with, say, a primary key header_ID, and some other attributes
I will be needing to flag those rows with different filters. I can't know in advance how many, but for most rows it will be between 0 to 10.
So, I thought of creating another table (let's call it filter) with attributes h_ID and filter_ID. So, if this table has the following it would mean that header_ID=2 was flagged with the filter 1 and 3, and header_ID=3 with filter 1
2 1
2 3
3 1
Then, another table with filter_ID and an attribute with some text describing the filter.
The basic query that I see myself doing often is, for example, "get certain rows from header that don't have any filters". Is this a design that makes these types of queries efficient? If so, how?
I was thinking about perhaps adding a filter_ID column to header, and replacing header_ID column with a filter_ID primary key, that will have value NULL in header when no filters have been assigned. Is that a better idea?
I appreciate your input
You can do a left join and then filter to only get rows with null values in the left table.
SELECT [cols]
FROM header
LEFT JOIN filters
ON header_id=h_id
WHERE [filter col] IS NULL
By the descriptions of your tables, it would be a pretty bad idea to have a filter column in the header table. It would lead to some pretty inefficient queries.
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...