Im creating a little database that has employee, emp_shift, shift, tables
now im suppose to be able to calculate at the end of the month which employee
has done the most number of shifts.
Ive created the SQL creation, insert statements for the tables, and a little diagram to explain what im trying to acomplish, im a beginner and this is a homework ive been trying to do for the last 4 days.
Diagram: http://latinunit.net/emp_shift.jpg
SQL: http://latinunit.net/emp_shift.txt
can you please guys check it, deadline is 2 days and this is just a part of the whole database
That is a reasonable start. Will you have more tables? If not, it will be hard to identify how to pay people -- for example, it seems that you might want a "pay-period" table. Then you could find the start and end dates and be able to count the shifts within that period.
But if all you need to do is exactly what you said, that is a fair start.
(I am assuming you have other columns in mind, such as employee name, but that would be obvious).
You could start by telling us whoch RDBMS you are using, as some of the finer details might be different between RDMSs.
You need to create a link between tables (Called JOINS, Read this) and then perform a count of the requested data.
After you have read some of these, show us what you have done, and we can help you where you are having trouble.
also, it would be better practive to use a single numeric as the primary key instead of 'A', 'B', 'C' etc.
Related
In my Qt C++ project I am using SQL database for table view. Everything is working fine, but now I need to create something bigger. I need to show name, school subject, and final assessment for this subject.
The problem is in that, that I've got about 45 subjects, and I need to repeat them twice cause there are 2 periods for each subject.
Do I need to create about 90 tables in SQL for each subject and each final assessment or is there some smarter and easier way?
The answer for your question is here: http://en.wikipedia.org/wiki/Entity%E2%80%93relationship_model
Read carefully and you are going to find out that you don't need to create one table for each subject.
Here's my application workflow.
I have a ref cursor that is populated with all my employees IDs..It's just an identification number really.
But now I want to fetch a lot of information for every employee...(as fetched form the ref cursor).It's not simply data, but a lot of computed,derived data too. The sort of derivation that's more easily done via cursors and procedures and so on....
For example, the sum of all the time intervals during which an employee was stationed in Department 78...(that could be just one of the columns for each employee).
So I think I could accomplish this with a really large (by large, I mean really difficult to maintain, difficult to understand, difficult to optimize, difficult to reuse, refactor..etc etc) SQL query, but that really isn't something I'd do unless as a real last resort.
So I'm trying to find ways to use all of PL/SQL's might to split this into as many separate units (perhaps functions or procedures) as possible so as to be able to handle this in a simple and elegant way...
I think that some way to merge datasets (ref cursors probably) would solve my problems... I've looked at some stuff on the internet until now and some things looked promising, namely pipelining... Although I'm not really sure that's what I need..
To sum up, what I think I need is some way to compose the resulting ref cursor(a really big table, one column for the ID and about 40 other columns, each with a specific bit of information about that ID's owner.),using many procedures, which I can then send back to my server-side app and deal with it. (Export to excel in that case.)
I'm at a loss really.. Hope someone with more experience can help me on this.
FA
I'm not sure if that is what you want, or how often do you need to run this thing
But since it sounds very heavy maybe you dont need the data up to date this second
If it's once a day or less, you can create a table with the employee ids, and use seperate MERGE updates to calculate the different fields
Then the application can get the data from that table
You can have a job that calculates this every time you need updated data.
You can read about the merge command here wiki and specifically for oracle here oracle. Since you use separate commands you can of course do it in different procedures if that is convenient.
for example:
begin
execute immediate 'truncate table temp_table';
insert into temp_table select emp_id from emps;
MERGE INTO temp_table a
USING (
select name ) b
on (a.emp_id = b.emp_id )
WHEN MATCHED THEN
UPDATE SET a.name = b.name; ...
Not understanding how to express a particular type of query with ActiveRecord's syntax.
Company
has_many shareprices
When the processes run to update the shareprices, a new entry is created in the shareprice table. So you obviously end up with lots of shareprice rows for each company. In such a scenario you could end up with 1 company having 5 very high share price entries in the last time period.
So let's say I want to return the companies that currently have the highest shareprice in the last time period - I need it to basically return the max price for that company from the shareprices table and then find the next.
I can't work out how to do that with ActiveRecord syntax. I've tried a lot of approaches inspired by other stackoverflow answers but invariably can't get it to return unique companies so I'm missing a point somewhere around select unique, joining, group by, or something else.
Environment: postgresSQL backend deploying to heroku.
Help very much appreciated.
Without knowing your structure it's hard to provide a concrete answer. But somthing like this should work.
Company.select('max(share_prices.price) as price,companies.id').joins(:share_prices).group(:id).order('price')
I'm given a task from a prospective employer which involves SQL tables. One requirement that they mentioned is that they want the name retrieved from a table called "Employees" to come in the form at of either "<LastName>, <FirstName>" OR "<FirstName> <MiddleName> <LastName> <Suffix>".
This appears confusing to me because this kind of sounds like they're asking me to make a function or something. I could probably do this in a programming language and have the information retrieved that way, but to do this in the SQL table exclusively is weird to me. Since I'm rather new to SQL and my familiarity with SQL doesn't exceed simple tasks such as creating databases, tables, fields, inserting data into fields, updating fields in records, deleting records in tables which meet a specific condition, and selecting fields from tables.
I hope that this isn't considered cheating since I mentioned that this was for a prospective employer, but if I was still in school then I could just outright ask a professor where I can find a clue for this or he would've outright told me in class. But, for a prospective job, I'm not sure who I would ask about any confusion. Thanks in advance for anyone's help.
A SQL query has a fixed column output: you can't change it. To achieve this. you could have a concatenate with a CASE statement to make it one varchar column, but then you need something (parameter) to switch the CASE.
So, this is presentation, not querying SQL.
I'd return all 4 columns mentioned and decide how I want them in the client.
Unless you have just been asked for 2 different queries on the same SQL table
You haven't specified the RDBMS, but in SQL Server you could accomplish this using Computed Columns.
Typically, you would use a View over the table..
In the project where I work I saw this structure in database, and I ask to all of you, what a hell of modeling is this?
TableX
Columns: isMonday, BeginingHourMonday, EndHourMonday, isTuesday, BeginingHourTuesday, EndHourTuesday and so on...
Is this no-sql? I did not asked to the personn who created becaus I'm ashamed :$
Bye.
this is totally de-normalized data. no-sql kind of. i just wonder why month is not included. it could increase the de-normalization-factor.
This is called a calendar table.
It is a very common and incredibly useful approach to dealing with and solving a lot of date and time related queries. It allows you to search, sort, group, or otherwise mine for data in interesting and clever ways.
#Brian Gideon is right. So is #iamgopal. And I am too, when I say "it depends on the nature of the data being modeled and stored in the database".
If it is a list of days with certain attributes/properties for each day, then yes, I would call it denormalized -- and 9 times out of 10 (or more) this will probably be the case. (I recall a database with 13 columns, one for each month in the year and one for total, and at the end of the year the user added 13 more columns for the next year. "Mr. Database", we called him.)
If this is a description of, say, work hours within a week, where each and every time the data is queried you always require the information for each day in the week, then the row would represent one "unit" of data (each column dependant upon the primary key of the table and all that), and it would be counter-productive to split the data into smaller pieces.
And, of course, it might be a combination of the two -- data that was initially normalized down to one row per day, and then intentionally denormalized for performance reasons. Perhaps 9 times out of 10 they do need a weeks' worth of information, and analysis showed massive performance gains by concatenating that data into one row?
As it is, without further information on use and rational I'm siding with #iamgopal, and upvoting him.
Looks like a structure of a timesheet for a given week.
If normalized, it might look like
columns: day, startHour, endHour
When this is converted to a pivot table in excel, you will have a timesheet kind of a structure, which is good for input screens/views (as against creating a view with normalized structure).
Looking to that table. I don't see any good reason to do that, even for a performance reason.
Lets see, if I change the isMonday, isTuesday, etc to ID_Day I still get the same speed and logic. And if I change the BeginingHourMonday to StartHour and the EndHourMonday to EndHour, I still get the same effect.
I still have the day of week and the start and end time and that is the basically idea I get from the table struture. Maybe there is something I'm not seeing.
Regards