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.
Related
I have to add a new table according to some new requirements, the model currently consists of two tables: DETAIL and SUMMARY.
The relation is that every detail has associated one summary, so now I need to add a new table called SUMMARY_ESP, which has the a FK ( SUMMARY) and two more columns, something like this:
ID | SUMMARY_ID | ESP_ID | PRIORITY_ESP | PTY_ID | PRIORITY_PTY
1 | 123 | 34 | 1 | 122 | 1
2 | 123 | 35 | 2 | 111 | 2
3 | 123 | 30 | 3 | null | null
4 | 1111 | 34 | 4 | null | null
Other tables info:
DETAIL TABLE
ID_DET | AMOUNT | DATE | ID_SUMMARY | EXTERNAL_ID
1 | 1000 | 14/05/2018 | 1111 | 4
2 | 2000 | 18/07/2016 | 1111 | 4
3 | 1200 | 11/07/2017 | 123 | 1
4 | 1300 | 21/09/2018 | 123 | 2
SUMMARY TABLE
ID_SUMMARY | PRIORITY| PROFILE | CLASS | AREA
123 | 1 | 1 | 5 | 3
1111 | 2 | 1 | 5 | 3
33 | 3 | 2 | 5 | 9
4 | 4 | 8 | 5 | 10
So according to this, SUMMARY_ID , ESP_ID and PTY_ID are unique, the thing is at some point to know the what is the ESP_ID of certain detail, but since the relation is with SUMMARY table, I have no idea which one was when it was added, so I was asked to create a new column to the DETAIL table called EXTERNAL_ID, so I can know what is the code from the SUMMARY_ESP.
So if the row is the first one, it can be either 24 or 122 in the new column according to some previous logic, but I'm worried about the implications this might have in the future, because somehow I might be duplicating information, also I would need to make some weird logic in order to get the priority depending on whether it's ESP_ID or PTY_ID.
The new table along with SUMMARY are somehow parameters table, their values do not change that often and only the PRIORITY column would change, DETAIL instead is more transactional, and it has insert and update everyday according to some business logic.
I was thinking of adding the ID of the new table as a FK to the DETAIL table, but at the end would be the same, because it'll be hard to maintain and update would be harder, also it's like a circular dependency, so I'm kind of stuck with this , so any kind of help would be really helpful, below the complete model, with the current idea.
Also I can't add those new columns to the table SUMMARY, because there could be more than one associated to the same code in that table and since it's the PK I cant add two rows with the same code.
The relation is that every detail has associated one summary
You need to represent that relationship in your database layout : if you have a 1-N relationship between SUMMARY and DETAIL, you want to create another column in DETAIL that holds the primary key of the SUMMARY record that it is related to.
With this relation in place, you can start from a DETAIL row, relate a row from SUMMARY and identifiy all SUMMARY_ESP records that are linked to it.
Now if you need to uniquely relate a DETAIL record to a SUMMARY_ESP record, then you want to either add a foreign key to SUMMARY_ESP in DETAIL, or the other way around (add a foreign key to DETAIL in SUMMARY_ESP), depending on the way your data flows.
As the questions states, what is the best way when designing a database for types and categories?
Scenario:
I have x amount of database-tables e.g. users, feedback, facts and countries, and all these tables have a type-attribute. What I've found is that a lot of people tend to just create type-tables for each and one of these. E.g. user_types, feedback_types, fact_types and country_types.
I'm currently working on a project where I don't want to create a bunch of extra tables just to handle their individual types. Therefore I'm trying to come up with a database-design-solution that fits all tables.
My best thought of solution:
At first I thought I might just create a polymorphic table that has id, type_id, typable_id and typable_type and a types table. Then i figured that I have to specify in the types table which type-attribute belongs to which table. Then it hit me, I can create a self-referencing table where the parent name is the table name.
E.g.
---------------------------------------------
|id | parent_id | name | description |
---------------------------------------------
| 1 | null | feedback | something |
---------------------------------------------
| 2 | 1 | general | something |
---------------------------------------------
| 3 | 1 | bug | something |
---------------------------------------------
| 4 | 1 | improvement | something |
---------------------------------------------
| 5 | null | countries | something |
---------------------------------------------
| 4 | 5 | europe | something |
---------------------------------------------
| 4 | 5 | asia | something |
---------------------------------------------
| etc... |
---------------------------------------------
Is this a ok design? I'm thinking a lot about the parent names in this table, I haven't seen anyone else use table-names as parents.
If thinking about it in a front-end point of view, it's easier to get the correct types depending on which types you're looking for.
Please give me feedback on this. I'm struggling to find a good design.
Let's assume we have application with pages, posts and events. With each part of this application we want to have comments. Now let's take a look into tables for our DB.
1. One comment table, object and object_id as foreign key
Page/Post/Event has many comments, foreign key object, object_id
comments table
+-------------+-------------+-------------+-------------+
| id | object | object_id | text |
=========================================================
| 1 | Page | 1 | Comment 1 |
+-------------+-------------+-------------+-------------+
| 2 | Post | 1 | Comment 2 |
+-------------+-------------+-------------+-------------+
| 3 | Event | 1 | Comment 3 |
+-------------+-------------+-------------+-------------+
2. Multiple comments tables
Page (Post, Event) has many page comments, foreign key page_id
page_comments table
+-------------+-------------+-------------+
| id | page_id | text |
===========================================
| 1 | 1 | Comment 1 |
+-------------+-------------+-------------+
post_comments table
+-------------+-------------+-------------+
| id | post_id | text |
===========================================
| 1 | 1 | Comment 2 |
+-------------+-------------+-------------+
event_comments table
+-------------+-------------+-------------+
| id | event_id | text |
===========================================
| 1 | 1 | Comment 3 |
+-------------+-------------+-------------+
I have used specific example, but this can apply to any other 1:N tables or even with M:N (tags), but for simple showcase, this should be good.
We should discuss
Performance concerns
Design pros and cons
Initial thoughts
case 1 means less tables in DB, easier to read, reusable application code
case 1 is better when doing query on all comments (would have to use union at case 2)
case 2 is better in regards of normalization (3NF)
case 2 is easier to backup (dump) parts of the system, e.g. pages itself with their comments
case 2 should be better with performance because less rows => faster
I am developing a database system. It is for a canoe club. The part of the database I am stuck on is assigning a member of the canoe club to a canoe qualification course when/if they undertake one.
Here is a stripped down view of my tables:
members
-------------------------------------
| memberID | first_name | last_name |
-------------------------------------
| 1 | John | Jacobs |
| 2 | Ellie | Graham |
| 3 | Paul | Abbot |
-------------------------------------
course_info
---------------------------------------
| courseID | course_name | Instructor |
---------------------------------------
| 1 | BCU Level 1 | Ryan Adams |
| 2 | BCU Level 2 | Ryan Adams |
| 3 | BCU Level 3 | Ryan Adams |
| 4 | BCU Level 4 | Ryan Adams |
| 5 | BCU Level 5 | Ryan Adams |
---------------------------------------
course_progress
-------------------------------
| memberID | courseID | grade |
-------------------------------
| 1 | 2 | 4 |
| 1 | 4 | 5 |
| 2 | 1 | 3 |
| 3 | 5 | 2 |
-------------------------------
So as you can see,course_progress displays the courses a member has undertaken as well as their grade by using memberID and courseID.
Firstly is that the correct (or a correct) way of doing this? If so, here is my problem...
Using Access I want to create a form that allows me to assign a member to a course. So I have a combo box that lists all of the members and another that lists all of the courses. As well as a box for inputting the grade.
When I fill in this form it only adds the grade to the course_progress table. I feel as though this is the case because I am using fields from different tables in the combo box. The other solution that while works is less than ideal is to have memberID and courseID in the combo box. I believe that works as I am using fields from the table I am trying to add to. However it is not user friendly as ID's are meaningless to a user.
So I want to be able to select the member name and course name from the combo box and add them to the course_progress table as well as the grade.
Any guidance would be great.
Thanks.
Firstly, is your form bound to the course_progress table., and are the two combo boxes bound to the memberID and courseID fields of the progress table.
Secondly, what have you used as the query for each combo box. You should be querying the members table. Assuming you do, you will have 3 columns, the first being the member ID and that should be the "bound column" in the combo box properties. in the format section you will need to give column widths, and I would give the memberID column a width of 0 so it doesn't show. But you should say you want to display 3 columns (so you get firstname and last name in the combo box.
Do the same for the course combo box.
I need to regularly import large (hundreds of thousands of lines) tsv files into multiple related SQL Server 2008 R2 tables.
The input file looks something like this (it's actually even more complex and the data is of a different nature, but what I have here is analogous):
January_1_Lunch.tsv
+-------+----------+-------------+---------+
| Diner | Beverage | Food | Dessert |
+-------+----------+-------------+---------+
| Nancy | coffee | salad_steak | pie |
| Joe | milk | soup_steak | cake |
| Pat | coffee | soup_tofu | pie |
+-------+----------+-------------+---------+
Notice that one column contains a character-delimited list that needs preprocessing to split it up.
The schema is highly normalized -- each record has multiple many-to-many foreign key relationships. Nothing too unusual here...
Meals
+----+-----------------+
| id | name |
+----+-----------------+
| 1 | January_1_Lunch |
+----+-----------------+
Beverages
+----+--------+
| id | name |
+----+--------+
| 1 | coffee |
| 2 | milk |
+----+--------+
Food
+----+-------+
| id | name |
+----+-------+
| 1 | salad |
| 2 | soup |
| 3 | steak |
| 4 | tofu |
+----+-------+
Desserts
+----+------+
| id | name |
+----+------+
| 1 | pie |
| 2 | cake |
+----+------+
Each input column is ultimately destined for a separate table.
This might seem an unnecessarily complex schema -- why not just have a single table that matches the input? But consider that a diner may come into the restaurant and order only a drink or a dessert, in which case there would be many null rows. Considering that this DB will ultimately store hundreds of millions of records, that seems like a poor use of storage. I also want to be able to generate reports for just beverages, just desserts, etc., and I figure those will perform much better with separate tables.
The orders are tracked in relationship tables like this:
BeverageOrders
+--------+---------+------------+
| mealId | dinerId | beverageId |
+--------+---------+------------+
| 1 | 1 | 1 |
| 1 | 2 | 2 |
| 1 | 3 | 1 |
+--------+---------+------------+
FoodOrders
+--------+---------+--------+
| mealId | dinerId | foodId |
+--------+---------+--------+
| 1 | 1 | 1 |
| 1 | 1 | 3 |
| 1 | 2 | 2 |
| 1 | 2 | 3 |
| 1 | 3 | 2 |
| 1 | 3 | 4 |
+--------+---------+--------+
DessertOrders
+--------+---------+-----------+
| mealId | dinerId | dessertId |
+--------+---------+-----------+
| 1 | 1 | 1 |
| 1 | 2 | 2 |
| 1 | 3 | 1 |
+--------+---------+-----------+
Note that there are more records for Food because the input contained those nasty little lists that were split into multiple records. This is another reason it helps to have separate tables.
So the question is, what's the most efficient way to get the data from the file into the schema you see above?
Approaches I've considered:
Parse the tsv file line-by-line, performing the inserts as I go. Whether using an ORM or not, this seems like a lot of trips to the database and would be very slow.
Parse the tsv file to data structures in memory, or multiple files on disk, that correspond to the schema. Then use SqlBulkCopy to import each one. While it's fewer transactions, it seems more expensive than simply performing lots of inserts, due to having to either cache a lot of data or perform many writes to disk.
Per How do I bulk insert two datatables that have an Identity relationship and Best practices for inserting/updating large amount of data in SQL Server 2008, import the tsv file into a staging table, then merge into the schema, using DB functions to do the preprocessing. This seems like the best option, but I'd think the validation and preprocessing could be done more efficiently in C# or really anything else.
Are there any other possibilities out there?
The schema is still under development so I can revise it if that ends up being the sticking point.
You can import you file in the table of the following structure: Diner, Beverage, Food, Dessert, ID (identity, primary key NOT CLUSTERED - for performance issues).
After this simply add the following columns: Dinner_ID, Beverage_ID, Dessert_ID and fill them according to your separate tables (it's simple to group each of the columns and to add the missing data to lookup tables as Beverages, Desserts, Meals and, after this, to fix the imported table with the IDs for existent and newly added records).
The situation with Food table is more complex because of ability to combine the foods, but the same trick can be used: you can also add the data to your lookup table and, among this, store the combinations of foods in the additional temp table (with the unique ID) and separation on the single dishes.
When the parcing will be finished, you will have 3 temp tables:
table with all your imported data and IDs for all text columns
table with distinct food lists (with IDs)
table with IDs of food per food combination
From the above tables you can perform the insertion of the parsed values to either structure as you want.
In this case only 1 insert (bulk) will be done to the DB from the code side. All other data manipulations will be performed in the DB.