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As you said An entity type is a broader classification that groups similar entities together, it contains structure and properties. An entity, we can see it as a single instance of entity type.
In ER diagrams we can use the rectangle labeled (e.g "St...
Given the statement
"Then group according to the creditcode for all the cases where 'EITHER' the
count is greater than 2 or the city or phone is not empty."
in the Question, we know that EACH of the following fulfilled SHOULD be listed
1. count(cust ...
What is the best way to identify fan trap and chasm trap in ER diagram early in the conceptual modelling designing stage?
Do I have to draw semantic net with some possible data to be able to identify it?
Hello
I'm having trouble distinguishing between an entity and an entity type .
The textbook says that an entity is a "distinct object that is to be represented in the database". The examples of entities it gives are
- Branch
- Staff
- PropertyF...
It is called UML (unified modeling language). Yes a ternary relationship is represented by a diamond.
However, entities are represented by rectangles. Please also make sure you know how multiplicities are represented.
Cheers.
ANONYMOUS wrote
Hi , I just wanted some clarification.
For this unit, we are only using EML notation for ER diagram right?
In EML notation, do we use diamond shape ? I saw in lecture slides where ternary relationship is presented in diamond shape.
Thanks
I was thinking it would be
SELECT creditcode, count(cust id) AS 'Number of Publishers'
FROM publishers
WHERE city IS NOT NULL OR phone IS NOT NULL
GROUP BY creditcode
HAVING COUNT(cust id) 2
ORDER BY creditcode;
Am I wrong?
Maybe because the city and phone condition arrears in the WHERE clause? (Since city and phone are column names only, not aggregate functions).
As far as I understand, if there are column names in the HAVING clause, they must be in the GROUP BY clause,...
Hi,
First of all I did not create this question, but let's try to solve it together.
Please see slides 33 if the lecture. The number of tuples in the resulting relation (after cartesian product is applied) are number of tuples in the first relation t...
Hi,
For our midterm and when drawing ER diagrams in general,do we have to know and use these arrows?Additionally,when writing down the multiplicity(1.. etc.) do we need to write it on top of the arrow or under the entity?Thanks for your help
hi,
I was doing this question and Im a bit confused on what answer is correct.When I was doing cartesian product of A,B from R and A,C from T it gives 8 tuples.However,we can also remove the 2 repeated tuples(1222 and 2222) which will give us 6 distin...
Hi,
1. While using sqlite, boolean datatypes are converted to integers. For this question you could have instead used an integer.
2. Pi underscore (column names), indicates which columns to display. Just writing the name of the relation without Pi mea...
Hi,
While I am practicing for the midterm exam, I have following questions
1. On worksheet 1, at the query for CREATE TABLE, I am not so sure about the type of isOwnerOccupied is BOOLEAN. As I look up on the internet, I don't think SQLite3 has type of...
So the final correct would be like this ?
...
SELECT creditcode, count(cust id) AS 'Number of Publishers'
FROM publishers
GROUP BY creditcode
HAVING COUNT(cust id) 2 AND (city IS NOT NULL OR phone IS NOT NULL)
ORDER BY creditcode;
...
Actually the reason this query can run
SELECT job id, po date FROM pos WHERE po date '1990-01-03' GROUP BY job id;
is Because sqlite have "bare columns" implementation in aggregation query
https www.sqlite.org draft lang select.html bare columns in ...
