We have R(A,B,C)
1 2 3
1 3 2
1 2 2
3 2 1
3 2 3
Question : Which of the following multivalued dependencies does this instance of R not satisfy?
BC ↠ A
BC ↠ C
C ↠ A
✔ A ↠ B
Right answer is 4 but why i dont understand
please explain
It doesn't satisfy statement 4 because for every unique combination of A and B, you have to have matching rows with C.
To make Statement 4 valid, you'd need a 1 3 3 in your table (since you have a 1 2 3).
Good luck.
Related
Hi I have a data set that looks like:
A1 A2 ... A100 Target
7 7 ... 2 2
2 2 ... 3 4
2 2 ... 2 4
2 2 ... 2 3
5 5 ... 2 7
I would like to find out which column among A{1, 2, ... 100} mostly correlates with Target column. If number of columns is small, I know I can simply do CORR for each of them, but in this case, what is the best practice? Thanks
I am trying to get those rows from the table which is corresponding to the selective indexes. For example, i have one xls file in which different columns of data. currently my code search the selective two columns and their indexes also, know i want to search those selective rows corresponding elements which is in different rows.
Lets A B C D E F G are columns name in which 1000 of rows of numbers
like
A B c D E F G
1 3 4 5 6 3 3
3 4 5 6 3 2 7
.............
4 7 3 2 5 3 2
So Currently my code search two specific columns (lets suppose B and F selective values which is in some range), now i want to search column A value which is present in those selective ranges.
B F A
3 4 5
3 5 3
7 7 3
5 4 6
...
like this
This is my current code VI
I hope we've finally gotten to the bottom of it. How about this one?
The teacher gave us a team assignment, and me and my teammate are quite struggling with it (especially since we need to use things like TRIGGERS and PROCEDURES, things we didn't see in class yet …).
We need to implement an arc-relationship, and we fail to understand how …
But before I tell you guys what I need to accomplish, I will give you part of the description of the task, so you guys can understand the situation a bit better …
We basically need to make an ERD for a VLSI CAD-system and we need to implement it. Now, we have our CELL entity, the attributes of which aren't really relevant … The only thing you guys need to know in order to help us is that it has a primary key, CELL_CODE, which is a VARCHAR.
Each CELL has many (I think at least four, I don't think you can have triangular CELLS, but doesn't matter anyways) SIDES. A SIDE can be logically identified by its CELL, and to make matters ridiculously difficult, each SIDE has to be numbered by its CELL, like so:
CELLS:
CELL_CODE
1
2
SIDES:
SEQUENCE_NUMBER CELL_CODE
1 1
2 1
3 1
1 2
2 2
3 2
Now, each SIDE has its CONNECTION_PINS. CONNECTION_PINS is also uniquely identified by SIDES, which are basically numbered in a similar manner:
CELLS:
CELL_CODE
1
2
SIDES:
SEQUENCE_NUMBER CELL_CODE
1 1
2 1
3 1
1 2
2 2
3 2
CONNECTION_PINS:
SEQUENCE_NUMBER SIE_SEQUENCE_NUMBER CELL_CODE
1 1 1
2 1 1
1 2 1
2 2 1
1 3 1
2 3 1
1 1 2
2 1 2
1 2 2
2 2 2
1 3 2
2 3 2
I tried to explain the numbering issue we have here: Data model - PRIMARY KEY numbering issue, but yeah, I didn't really explain it the way it should be explained ...
Now, we have one final entity, which is where the Arc comes in: CONNECTIONS. CONNECTIONS has 2 CONNECTION_PINS: one for START_FROMand one for END_OF. Now, logically seen the start pin can't be the end pin as well, for a given connection. And that's our struggle. Basically, this shouldn't be allowed:
CELLS:
CELL_CODE
1
2
SIDES:
SEQUENCE_NUMBER CELL_CODE
1 1
2 1
3 1
1 2
2 2
3 2
CONNECTION_PINS:
SEQUENCE_NUMBER SIE_SEQUENCE_NUMBER CELL_CODE
1 1 1
2 1 1
1 2 1
2 2 1
1 3 1
2 3 1
1 1 2
2 1 2
1 2 2
2 2 2
1 3 2
2 3 2
CONNECTIONS:
(you shouldn't be able to put this in …)
CPI_SEQNUM_START SIE_SEQNUM_START CELL_CODE_START CPI_SEQNUM_END SIE_SEQNUM_END CELL_CODE_END
1 1 1 1 1 1
Now, this is basically the ERD for this part:
ERD with barred relationships and the arc-relationship in question
and this is the physical model:
Physical model
I basically thought a simple CHECK might do (CHECK (CPI_SEQNUM_START <> CPI_SEQNUM_END AND CELL_CODE_START <> CELL_CODE_END AND SIE_SEQNUM_START <> SIE_SEQNUM_END) ), but that prevented us from inserting anything somehow … Any advice?
Your approach was correct to use a CHECK constraint. Your logic for the constraint was wrong though. You need an OR condition. Only one of the three fields needs to be different.
CPI_SEQNUM_START <> CPI_SEQNUM_END OR
CELL_CODE_START <> CELL_CODE_END OR
SIE_SEQNUM_START <> SIE_SEQNUM
... assuming all three fields are not nullable.
I have a requirement from client where I need to store a value against list of combination.
For example I have following LOBs and against each combination I need to store a value.
Auto
WC
Personal
I purposed multiple solutions he is not satisfied with anyone.
Solution 1: create single table, insert value against all possible combination(string) something like
LOB Value
Auto 1
WC 2
Personal 3
Auto,WC 4
Auto, personal 5
WC, Personal 6
Auto, WC, Personal 7
Solution 2: create lkp_lob, lob_group and lob_group_detail tables. Each group combination represent a group.
Lkp_lob
Lob_key Name
1 Auto
2 WC
3 Person
Lob_group (unique query constrain on lob_group_key and lob_key)
Lob_group_key Lob_key
1 1
2 2
3 3
4 1
4 2
5 1
5 3
6 2
6 3
7 1
7 2
7 3
Lob_group_detail
Lob_group_key Value
1 1
2 2
3 3
4 4
5 5
6 6
7 7
Any suggestion would be highly appreciated.
First of all I did not understood that terms you said.
But from database perspective it is always good to have multiple tables for each module. You will be facing less difficulties when doing CRUD. And will be more faster.
I have a track and Field Database with these tables (simplified):
Performance Table
Row Athlete Event Mark Meet
1 1 3 0:55 A
2 2 2 2:25 A
3 3 3 0:54 A
4 4 4 4:10 A
5 2 2 2:11 A
6 3 2 2:12 B
7 1 1 10 C
Athlete Table
Row Name Age Sex
1 Joe 13 M
2 Amy 15 F
3 John 16 M
4 Tim 17 M
So I understand how to implement this for an event with only 1 athlete (e.g. 100 m dash), but how would I include a relay event with 4 athletes. So, for example a 4x400 relay would need 4 athletes. In other words, some events have only 1 athlete and some have more than one. I am not sure if I should use:
Linking Table
Add 4 Columns
Do a table like below.
Other
Option 3 Table
Performance Table (Event 5 is a relay)
Row Athlete Event Mark Meet
1 1 3 0:55 A
2 2 2 2:25 A
3 3 3 0:54 A
4 4 4 4:10 A
5 2 2 2:11 A
6 3 2 2:12 B
7 1 5 9:34 C
8 2 5 9:34 C
9 3 5 9:34 C
10 4 5 9:34 C
Are you going to have events in the system before they are finished? For example, today's meet will include a 4x400 and here are the runners...
If that's the case then you'll need the linking table that you referred to because you want to be able to have that data stand on its own. It would just have the event_id and athlete_id in it so that you could have that set up. That would also be the PK (Primary Key) for the table and you would then use those two columns as the FK (Foreign Key) to the Performance table that you have at the end. If the data will never exist without times then you could just skip the link table and have the Performance table, although having the link table still wouldn't hurt in that case.