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.
Related
I am trying to select a number of rows by the value of a column called ID. I know you can do this pretty easily by:
SELECT col1, col2, col3 FROM mytable WHERE id IN (1,2,3,4,5...)
However, what if there are a few million IDs I want to select and the IDs don't always have pattern (which means I can't use something like BETWEEN x AND y)? Does this select statement still work or is there better ways of doing so?
The actual application is this. Filters are specified by users, which is compared to some attributes of the records. From those filters, we create a subset of the data which is of interest to a particular user. There are about 30 million records each with roughly ~3000 attributes (which is stored in roughly 30 tables, but every table has ID as a primary key), so every time someone makes a query about their desired subset of records, we'd have to join many tables, apply those filters, and figure out what his subset looks like. In order to avoid joining many tables all the time, I thought maybe it's a better idea to join the tables once, figure out the id of the selected subset, and this way each time a new query is made, all we have to do is select the relevant columns of the rows that match the filtered ids.
This depends on the database and the interface you are using. For a few hundred or thousand values, no problem. But your question specifies millions. And that could start to get into limits on the length of the query -- either specified by the database, the tool you are using, or intermediate libraries.
If you have so many ids, I would strongly recommend that you load them into a table in the database with the id as the primary key. Then use join or exists to identify the rows in your table that match.
Often, such a list would be generated in the database anyway. In that case, you can use a subquery or CTE and just include that code in your final query.
I have a table joined from two other tables. I would like this table to stay updated with entries in the other two tables.
First Table is "employees"
I am using the ID, Last_Name, and First_Name.
And the second Table is "EmployeeTimeCardActions"
using columns ID, ActionTime, ActionDate, ShiftStart, and ActionType.
ID is my common column that the join was created by..Joined Table...
Because I usually have a comment saying I did not include enough information, I do not need a exact specific code sample and I think I have included everything needed. If there is a good reason to include more I will, I just try to keep as little company information public as possible
Sounds like you're having your data duplicated across tables. Not a smart idea at all. You can update data in one table when a row is updated in a different one via triggers but this is a TERRIBLE approach. If you want to display data joined from 2 tables, the right approach here is using an SQL VIEW which will display the current data.
I have a very large database I would like to split up into tables. I would like to make it so when I run a distinct, it will make a table for every distinct name. The name of the table will be the data in one of the fields.
EX:
A --------- Data 1
A --------- Data 2
B --------- Data 3
B --------- Data 4
would result in 2 tables, 1 named A and another named B. Then the entire row of data would be copied into that field.
select distinct [name] from [maintable]
-make table for each name
-select [name] from [maintable]
-copy into table name
-drop row from [maintable]
Any help would be great!
I would advise you against this.
One solution is to create indexes, so you can access the data quickly. If you have only a handful of names, though, this might not be particularly effective because the index values would have select almost all records.
Another solution is something called partitioning. The exact mechanism differs from database to database, but the underlying idea is the same. Different portions of the table (as defined by name in your case) would be stored in different places. When a query is looking only for values for a particular name, only that data gets read.
Generally, it is bad design to have multiple tables with exactly the same data columns. Here are some reasons:
Adding a column, changing a type, or adding an index has to be done times instead of one time.
It is very hard to enforce a primary key constraint on a column across the tables -- you lose the primary key.
Queries that touch more than one name become much more complicated.
Insertions and updates are more complex, because you have to first identify the right table. This often results in overuse of dynamic SQL for otherwise basic operations.
Although there may be some simplifications (security comes to mind), most databases have other mechanisms that are superior to splitting the data into separate tables.
what you want is
CREATE TABLE new_table
AS (SELECT .... //the data that you want in this table);
I have an array of 50+ elements that dictates how many hours were worked for a given week.
What is the proper way to store this information into a database table?
My initial idea was to use a delimiter, but the text is too large (280 characters) to fit.
Additionally, there seems something "wrong" with creating a table column for each element.
Ideas?
Array using delimiter (comma):
37.5,37.5,37.5,37.5,37.5,37.5,37.5,37.5,37.5,37.5, ...
The "proper" way is to store the array's contents as multiple rows in a whole other table, each with a foreign key referencing the record they belong to back in the first table. There may be other things that work for you, though.
[EDIT]: From the details you added I'm guessing your array elements consist of a number of hours worked each week and you have 50+ of them because a year has 52-ish weeks. So what I think you're looking for, is I guess that your current (main) table is called something like "employees," is that each row there should have some unique identifier for each employee record. So your new table might be called "work_weeks" and consist of something like employee_id (which matches the employee id in the current table), week_number, and hours_worked.
Seems like a 1 to many relationship. For this example, tableA is the 1 and tableBlammo is the many.
tableA => column blammoId
tableBlammo => column blammoId, column data
One row in tableA joins to multiple rows in tableBlammo via the blammoId column.
Each row in tableBlammo has one element of the array in the data column.
I have an Access database of information where I need to replace text that may reside in 1 of 10 columns. I have a number of different requests for find and replace that need to be done. I need to do this twice a day.
These are the details. We receive a download of data twice a day that has course information in it. A record can have 10 courses in it. Some of the courses need to be combined. For instance
Course 1 is 12345, there are 2 other courses that are the same and therefore course 2(01234), Course 3(34566) all need to be changed to 12345. I also need to combine other course in a similar fashion, since I need to do this twice a day, ideally I would like to have a table with just columns of find and replace and use it to pick up the changes and reference it in my sql code.
An easy way to do this is the key!
Have you considered a cross reference table of something like
Table1
MCourse Subcourse
12345 2(01234)
12345 3(34566)
Then you can do updates like
Set mainTable.Desiredfield = Table1.Mcourse
where desiredfield = subcourse
Or you can create a query that uses the cross reference table to select the desired value and make a new table from that.