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.
Related
Hey guys, maybe this is a basic SQL qn. Say I have this very simple table, I need to run a simple sql statement to return a result like this:
Basically, the its to dedup Name based on it's row's Value column, whichever is larger should stay.
Thanks!
Framing the problem correctly would help you figure it out.
"Deduplication" suggests altering the table - starting with a state with duplicates, ending with a state without them. Usually done in three steps (getting the rows without duplicates into temp table, removing original table, renaming temp table).
"Removing rows with duplicated column values" also suggests alteration of data and derails train of thought.
What you do want is to get the entire table, and in cases where the columns you care about have multiple values attached get the highest one. One could say... group by columns you care about? And attach them to the highest value, a maximum value?
select id,name,max(value) from table group by id,name
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 have a table where I have these fields:
id(primary key, auto increment)
car registration number
car model
garage id
and 31 fields for each day of the mont for each row.
In these fields I have char of 1 or 2 characters representing car status on that date. I need to make a query to get number of each possibility for that day, field of any day could have values: D, I, R, TA, RZ, BV and LR.
I need to count in each row, amount of each value in that row.
Like how many I , how many D and so on. And this for every row in table.
What best approach would be here? Also maybe there is better way then having field in database table for each day because it makes over 30 fields obviously.
There is a better way. You should structure the data so you have another table, with rows such as:
CarId
Date
Status
Then your query would simply be:
select status, count(*)
from CarStatuses
where date >= #month_start and date < month_end
group by status;
For your data model, this is much harder to deal with. You can do something like this:
select status, count(*)
from ((select status_01 as status
from t
) union all
(select status_02
from t
) union all
. . .
(select status_31
from t
)
) s
group by status;
You seem to have to start with most basic tutorials about relational databases and SQL design. Some classic works like "Martin Gruber - Understanding SQL" may help. Or others. ATM you miss the basics.
Few hints.
Documents that you print for user or receive from user do not represent your internal data structures. They are created/parsed for that very purpose machine-to-human interface. Inside your program should structure the data for easy of storing/processing.
You have to add a "dictionary table" for the statuses.
ID / abbreviation / human-readable description
You may have a "business rule" that from "R" status you can transition to either "D" status or to "BV" status, but not to any other. In other words you better draft the possible status transitions "directed graph". You would keep it in extra columns of that dictionary table or in one more specialized helper table. Dictionary of transitions for the dictionary of possible statuses.
Your paper blank combines in the same row both totals and per-day detailisation. That is easy for human to look upon, but for computer that in a sense violates single responsibility principle. Row should either be responsible for primary record or for derived total calculation. You better have two tables - one for primary day by day records and another for per-month total summing up.
Bonus point would be that when you would change values in the primary data table you may ask server to automatically recalculate the corresponding month totals. Read about SQL triggers.
Also your triggers may check if the new state properly transits from the previous day state, as described in the "business rules". They would also maybe have to check there is not gaps between day. If there is a record for "march 03" and there is inserted a new the record for "march 05" then a record for "march 04" should exists, or the server would prohibit adding such a row. Well, maybe not, that is dependent upon you business processes. The general idea is that server should reject storing any data that is not valid and server can know it.
you per-date and per-month tables should have proper UNIQUE CONSTRAINTs prohibiting entering duplicate rows. It also means the former should have DATE-type column and the latter should either have month and year INTEGER-type columns or have a DATE-type column with the day part in it always being "1" - you would want a CHECK CONSTRAINT for it.
If your company has some registry of cars (and probably it does, it is not looking like those car were driven in by random one-time customers driving by) you have to introduce a dictionary table of cars. Integer ID (PK), registration plate, engine factory number, vagon factory number, colour and whatever else.
The per-month totals table would not have many columns per every status. It would instead have a special row for every status! The structure would probably be like that: Month / Year / ID of car in the registry / ID of status in the dictionary / count. All columns would be integer type (some may be SmallInt or BigInt, but that is minor nuancing). All the columns together (without count column) should constitute a UNIQUE CONSTRAINT or even better a "compound" Primary Key. Adding a special dedicated PK column here in the totaling table seems redundant to me.
Consequently, your per-day and per-month tables would not have literal (textual and immediate) data for status and car id. Instead they would have integer IDs referencing proper records in the corresponding cars dictionary and status dictionary tables. That you would code as FOREIGN KEY.
Remember the rule of thumb: it is easy to add/delete a row to any table but quite hard to add/delete a column.
With design like yours, column-oriented, what would happen if next year the boss would introduce some more statuses? you would have to redesign the table, the program in many points and so on.
With the rows-oriented design you would just have to add one row in the statuses dictionary and maybe few rows to transition rules dictionary, and the rest works without any change.
That way you would not
How to select only specific number of columns from a table in hive. For Example, If I have Table with 50 Columns, then how Can I just select first 25 columns ? Is there any easy way to do it rather than hard coading the column names.
I guess that you're asking about using the order in which you defined your columns in your CREATE TABLE statement. No, that's not possible in Hive for the moment.
You could do the trick by adding a new column COLUMN_NUMBER and use that in your WHERE statements, but in that case I would really think twice of the trade off between spending some more time typing your queries and messing your whole table design by adding unnecessary columns. Apart from the fact that if you need to change your table schema in the future (for instance, by adding a new column), adapting your previous code with different column numbers would be painful.
I have a table, and there is no column which stores a field of when the record/row was added. How can I get the latest entry into this table? There would be two cases in this:
Loop through entire table and get the largest ID, if a numeric ID is being used as the identifier. But this would be very inefficient for a large table.
If a random string is being used as the identifier (which is probably very, very bad practise), then this would require more thinking (I personally have no idea other than my first point above).
If I have one field in each row of my table which is numeric, and I want to add it up to get a total (so row 1 has a field which is 3, row 2 has a field which is 7, I want to add all these up and return the total), how would this be done?
Thanks
1) If the id is incremental, "select max(id) as latest from mytable". If a random string was used, there should still be an incremental numeric primary key in addition. Add it. There is no reason not to have one, and databases are optimized to use such a primary key for relations.
2) "select sum(mynumfield) as total from mytable"
for the last thing use a SUM()
SELECT SUM(OrderPrice) AS OrderTotal FROM Orders
assuming they are all in the same column.
Your first question is a bit unclear, but if you want to know when a row was inserted (or updated), then the only way is to record the time when the insert/update occurs. Typically, you use a DEFAULT constraint for inserts and a trigger for updates.
If you want to know the maximum value (which may not necessarily be the last inserted row) then use MAX, as others have said:
SELECT MAX(SomeColumn) FROM dbo.SomeTable
If the column is indexed, MSSQL does not need to read the whole table to answer this query.
For the second question, just do this:
SELECT SUM(SomeColumn) FROM dbo.SomeTable
You might want to look into some SQL books and tutorials to pick up the basic syntax.