Lets say I have a table that shows attendence to a lecture. The table is very simple, it only contains the date of the lecture, and the attendees.
2016-10-10 | Adam
2016-10-10 | Mike
2016-10-10 | David
2016-10-11 | Adam
2016-10-14 | Adam
2016-10-14 | David
What I would like is a query to show what percentage of the attendees for each lecture that was present on the previous lecture. Can this be done in a effective way?
The expected result would be something like this:
2016-10-11 | 1.00
2016-10-14 | 0.50
2016-10-10 would be left out since it does not have a previous lecture.
Related
My question is a bit simple, there are many answers to it but I have a question more about the query itself for certain conditions.
I have a table like this :
Client | Date | Employee | Last Record | Trained
JOE | April 2020 | John Doe | May 2019 | TRUE
JOE |February 2020| John Doe | May 2019 | TRUE
JOE | May 2 019 | John Doe | May 2019 | FALSE
Now I watn to make a simple SQL summary table saying :
Client | Date | Inactive | Trained
JOE | April 2020 | 1 | 1
JOE |February 2020 | 1 | 1
JOE | May 2019 | 0 | 0
So basically do a count of Employees grouped by client and date, with the condition that the difference of date and last record is greater than, lets say 1 month and also in another column count the number of employees with a TRUE condition.
So my question is basically that, hwo would I go about creating a summary table where I want to set conditions per column, such as a date difference or if its true in a column.
Before you say Use a view, I need to create this table for performance reason since I am querying the first table which has millions of rows for a report program. However it is simple and better to query instead a table that holds a summary or counts with conditions.
Temporal tables and time periods are nothing special in the IT world. But somehow it seems my request is rather unique because I cannot find anything useful for it at all.
What I have are two tables, one containing static data and the other one dynamic data for entries of the first table which changes over time. For each row in the second table there are two columns ValidFrom and ValidUntil whereas the latter can be null if there is no planned end of validity.
Simplified, the schema looks like this:
tbStatic
+----+------------+------------+
| Id | Attribute1 | Attribute2 |
+----+------------+------------+
| 1 | foo | bar |
| 2 | baz | foo |
+----+------------+------------+
tbDynamic
+----+------------+---------------------+---------------------+------------+------------+
| Id | tbStaticId | ValidFrom | ValidUntil | Attribute1 | Attribute2 |
+----+------------+---------------------+---------------------+------------+------------+
| 1 | 1 | 2018-01-01 00:00:00 | 2018-01-31 23:59:59 | 1 | 0 |
| 2 | 2 | 2018-04-01 00:00:00 | 2018-04-02 11:59.59 | 2 | 1 |
| 3 | 1 | 2018-02-01 00:00:00 | null | 2 | 1 |
| 4 | 2 | 2018-05-01 00:00:00 | 2018-06-01 00:00:00 | 23 | 15 |
| 5 | 2 | 2018-07-01 01:23:45 | 2018-07-05 23:12:01 | 80 | 12 |
+----+------------+---------------------+---------------------+------------+------------+
As you might have spotted, there is the possibility that we have holes between time periods. What we cannot have is overlapping periods, though. This means it is impossible to have overlapping time periods for the same tbStaticId.
Unfortunately, this is only a requirement until now and although it is enforced in the application using the database, I would prefer having a constraint on the table that prevents new rows to be inserted or existing rows to be updated when they violate this time uniqueness.
As stated, my research up to this point was rather disappointing and that is also the reason I cannot really show any code I've tried yet. The most promising approach I followed yet was to create a function that takes a record or the two time period values and the foreign key as input and determines if they overlap with something else. This function could then be called in a check constraint. But after thinking about the amount of cases to check, I gave up because it seemed unreasonable (especially when considering updates as well, which require additional attention).
So my question is if there is some easy way to constraint time slices in SQL Server, without the use of temporal tables (not available in my SQL Server version)? And if yes, how?
I am pretty new to database development and architecture. My only experience has been in college and now my project requires me to use that knowledge, however my project seems a lot more complicated with many more intricacies than what I studied.
A brief overview: My task is to basically turn paper work that was previously done by hand, into a quick computer application, which I will do in Java but thats far off now. I know I will need a database set up to accomplish my task since these reports are frequently edited. The report is a Labor Report. Basically, it shows who was working on a specific job, what days and how many hours on those days, as well as their total hours, pay rate, and total amount.
I believe my current problem lies within the fact that it seems like I'm going to have several "many to many" relationships, perhaps even nested, which is what is throwing my head for a spin as I try to organize information into entity relationship diagrams and tables. (I know that there are normally much more measured and organized stages to development but I don't have that experience and I'm essentially a one man team on this)
Contract Personnel with be selected out of a pool of Employees.
A Labor Contract can have 1 to 10 personnel (For sake of space on the final printed version, jobs requiring more laborers will have another Labor Contract.)
Each personnel must have 1 Title (foreman, mechanic, etc.) These titles can change from job to job. Joe Smith can be a mechanic on job A but a foreman on job B.
Each personnel must also have on record the number of hours they worked on each day of the week; and may have overtime and double overtime. (One Labor Record per week).
I am trying to avoid repeated data, or at least keep it to a minimum but I am struggling on figuring out how to do that in this situation. The tricky thing, at least in my mind, is figuring out how to handle the fact that different employees can work several jobs at once, under different titles, and different pay rates, and recording different types of hours (straight time, OT, double OT) on each day of the week.
Can anyone make suggestions?
I hope that I have supplied adequate information and apologize if I didn't or wasn't detailed enough. Please remember to keep in mind I'm a newbie to this type of work.
First thing, take a deep breath! It looks to me like you have a pretty good handle on this, maybe more than you think! This is not at all to try and design your project, and I'm sure you'll have lots of details to deal with, but maybe this will give an idea of how you might face these many many-to-many relationships swimming around in your head.
EMPLOYEES
---------
emp_id
emp_name
emp_address
JOBS
----
job_id
job_description
EMPLOYEE_JOBS
-------------
ej_id -- primary key
emp_id -- fk to employees table
job_id -- fk to jobs table
ej_title -- employee title for this job
ej_rate -- employee pay rate for this job
EMPLOYEE_JOB_HOURS
------------------
ejh_id -- primary key
ej_id -- fk to employee_jobs table
ejh_date
ejh_normal_hours -- hours worked by the employee on this job on this date, etc.
ejh_overtime_hours
ejh_double_overtime_hours
Following is a basic outline you could use to get started. Your final solution will be different based on your exact needs.
You'll need a table to store contract information. My example just shows a description but I'm sure you'll have much more than that.
contracts
id unsigned int(P)
description varchar(50)
+----+-------------+
| id | description |
+----+-------------+
| 1 | Contract A |
| 2 | Contract B |
| .. | ........... |
+----+-------------+
You'll need a table that links contracts and employees and shows what title the employee has for the given contract. In my example you can see that for Contract A John Q Public is a Foreman and Mary Jane Smith is a Mechanic. For Contract B their titles are reversed, John is a Mechanic and Mary is a Foreman. contract_id and employee_id are foreign keys to their respective tables and together they form the primary key. If it's possible that John and Mary get paid different rates for the same title (for example John get 25.00/hour as Foreman while Mary gets 20.00/hour) you would add a column here instead of using the rate in the titles table.
contracts_employees
contract_id unsigned int(F contracts.id)--\_(P)
employee_id unsigned int(F employees.id)--/
title_id varchar(15)(F titles.id)
+-------------+-------------+----------+
| contract_id | employee_id | title_id |
+-------------+-------------+----------+
| 1 | 1 | Foreman |
| 1 | 2 | Mechanic |
| 2 | 1 | Mechanic |
| 2 | 2 | Foreman |
| ........... | ........... | ........ |
+-------------+-------------+----------+
You'll need a table for employees (you could call this personnel if you prefer). You'll probably store a lot more than just their names...
employees
id unsigned int(P)
first_name varchar(30)
middle_name varchar(30)
last_name varchar(30)
...
+----+------------+-------------+-----------+-----+
| id | first_name | middle_name | last_name | ... |
+----+------------+-------------+-----------+-----+
| 1 | John | Quincy | Public | ... |
| 2 | Mary | Jane | Smith | ... |
| .. | .......... | ........... | ......... | ... |
+----+------------+-------------+-----------+-----+
You'll need a table to track hours worked. I just store a beginning and ending date/time, leaving it up to the application to calculate elapsed time. Your application will also need to ensure there is no overlap for employees - an employee should not be able to be working on more than one contract at any given time. Calculation of overtime and double overtime hours is also up to your application. If an employee's pay rate can change at any time (ie in the middle of a contract) you would want to store the pay rate in this table instead of using the rate from contracts_employees or titles.
hours
id unsigned int(P)
contract_id unsigned int(F contracts.id)
employee_id unsigned int(F employees.id)
beg datetime
end datetime
+----+-------------+-------------+---------------------+---------------------+
| id | contract_id | employee_id | beg | end |
+----+-------------+-------------+---------------------+---------------------+
| 1 | 1 | 1 | 2014-01-01 08:00:00 | 2014-01-01 17:00:00 |
| 2 | 1 | 2 | 2014-01-01 09:00:00 | 2014-01-01 17:30:00 |
| 3 | 1 | 1 | 2014-01-02 09:00:00 | 2014-01-02 10:00:00 |
| 4 | 1 | 2 | 2014-01-02 08:00:00 | 2014-01-02 09:00:00 |
| 5 | 2 | 1 | 2014-01-02 10:00:00 | 2014-01-02 17:30:00 |
| 6 | 2 | 2 | 2014-01-02 09:00:00 | 2014-01-02 15:00:00 |
| .. | ........... | ........... | ................... | ................... |
+----+-------------+-------------+---------------------+---------------------+
And finally a table to store titles and their related pay rates. If employees can be paid different rates for the same title, you wouldn't need the rate column here, instead you would use the rate stored in the contracts_employees table.
titles
id varchar(15)(P)
rate double
+----------+-------+
| id | rate |
+----------+-------+
| Foreman | 20.00 |
| Mechanic | 15.00 |
| ........ | ..... |
+----------+-------+
I have the following table below and am supposed to convert it to 2NF.
I have an answer to this where I have gone:
SKILLS: Employee, Skill
LOCATION: Employee, Current Work
Location
I have a feeling I'm wrong with this ^above^ though.
Also can someone explain what the differences are between 1NF, 2NF and 3NF. I know 1 comes first and you have to break it all up into smaller tables but would like a really good description to help me understand better. Thanks
I am new to learning 2NF but I have solved the answer like this. Let me know if this is correct so that I can understand my mistake and practice more.
Only two tables. Thanks
Employee Table
EmployeeID | Name
1 | Jones
2 | Bravo
3 | Ellis
4 | Harrison
Skills Table
SkillId | Skill
1 | Typing
2 | Shorthand
3 | Whittling
4 | Light Cleaning
5 | Alchemy
6 | Juggling
Location Table
LocationId | Name
1 | 114 Main Street
2 | 73 Industrial Way
EmployeeSkill Table
EmployeeId | LocationId | SkillId | SkillName
1 | 1 | 1 | Typing
1 | 1 | 2 | Shorthand
1 | 1 | 3 | Whittling
2 | 2 | 4 | Light Cleaning
3 | 2 | 5 | Alchemy
3 | 2 | 6 | Juggling
4 | 2 | 4 | Light Cleaning
In the EmployeeSkill table the primary key would be EmployeeId + LocationId, this gives you the skill they have at that location. Including the SkillName column violates 3NF in this example.
This practice is actually used sometimes in database design (and called "denormalization") in order to reduce joins to increase performance reading data that is commonly used together.
Ususally this is only done in tables used for reporting.
Hallo,
I need to merge users from several souces some how, for example facebook, Google, plaxo...
Currently I have this structure in my database:
USERS_MYSITE
mysite_user_id | parameter | value
------------------------------------------
223 | firstname | Tom
223 | lastname | N.
223 | birthdate | 1985-01-30
USERS_FACEBOOK
mysite_user_id | facebook_user_id | parameter | value
-------------------------------------------------------------
223 | 456353453 | fname | Tom
223 | 456353453 | lname | N.
223 | 456353453 | birth | 1985-01-30
USERS_GOOGLE
mysite_user_id | google_user_id | parameter | value
-----------------------------------------------------------
223 | tomtom22 | fn | Tom
223 | tomtom22 | ln | N.
223 | tomtom22 | brt | 1985 JUN 30
USERS_VIEW
mysite_user_id | remote_user_id | site_name | parameter | value
---------------------------------------------------------------------------
223 | 223 | mysite | firstname | Tom
223 | 223 | mysite | lastname | N.
223 | 223 | mysite | birthdate | 1985-01-30
223 | tomtom22 | google | fn | Tom
223 | tomtom22 | google | ln | N.
223 | tomtom22 | google | brt | 1985-01-30
223 | 456353453 | facebook | fname | Tom
223 | 456353453 | facebook | lname | N.
223 | 456353453 | facebook | birth | 1985 JUN 30
Then SELECT FROM USERS_VIEW WHERE mysite_user_id = '223' and i got all user information. After that i can use several transporation arrays, to transform all remote data to my format
Array("firstname" => Array("fn", "fname"), "birthdate" => Array("brt", "birth"), ...)
same goes with values. Next depending on what user selected as his primary data i can show it.
Problem is that I've never done it before, so maybe somebody knows how to do it better. Please share your ideas.
Thank you.
the idea was to create a engine, which could combine many accounts from many different "account holders", with possibility to add new if needed. Plus, give possibility to user customize his account data; to take first name from one source, last name from another and add from profile form. I worried about query speed, cause it's quite risky to make such slow query every time for every user shown on screen. Also we get a big traffic, about 1 million a day, that's 20 million page views, and about 100 000 000 query executions. That's a big count.
Yes, the problem is already solved. I just created another table, with duplicated data :( .
Every time user changes some of his settings a new table take update from structure above. Then we taking data only from that new table, and that method works fine. Already added linked in and twitter to sources list. Currently thinking to export that engine and make it open source. :)
You've probably already solved your problem by now - but in case you still need help, I'm happy to help. This is the kind of problem I like.
But in order to help, can you tell me what final outcome you actually want? You've got a solution that should work and I'm not sure if you're saying that you want it to produce a different outcome or that you want it to produce the current outcome but more efficiently?
If you can clarify that, we can sort this out.