WGU CS1011 Sophia Introduction to Relational Databases Milestone 2.

UNIT 2 — MILESTONE 2

20/25

20/25  that's 80% RETAKE



 20 questions were answered correctly.
4 questions were answered incorrectly.
1 question was skipped. These were marked incorrect.



1 


In each milestone, you may want or need to use the database
and query tool to answer some of the questions. We suggest you
open the tool in another browser tab while you are working on
this assessment.

https://postgres.sophia.org/

Which of the following is true of foreign keys?



Tables could be created first to
avoid having to create foreign
 
keys in order.



A foreign key should always be
linked to a primary key of another
 
table.



A foreign key can be linked to
 any foreign key.

, UNIT 2 — MILESTONE
A foreign 2 if the
key is not needed
 data type is different.
20/25

RATIONALE
In most cases, a foreign key should be linked to a candidate key
that is generally a primary key or a unique key. Foreign keys could
be temporarily disabled to simplify dropping the tables or moving
valid data. Foreign keys could also be added after tables have
been created to avoid having to generate them in the right order.

CONCEPT
 Foreign and Primary Keys

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2 


In each milestone, you may want or need to use the database
and query tool to answer some of the questions. We suggest you
open the tool in another browser tab while you are working on
this assessment.

https://postgres.sophia.org/

Which of the following is the valid syntax for creating a VIEW to
view a subset of a table?



CREATE VIEW album_cost
AS track

GROUP BY album_id;

, UNIT 2 — MILESTONE
CREATE 2
VIEW album_cost
AS
SELECT album_id, 20/25

SUM(unit_price)
GROUP BY album_id;



CREATE VIEW album_cost
SELECT album_id,
SUM(unit_price)

FROM track
GROUP BY album_id;



CREATE VIEW album_cost
AS
SELECT album_id,
  SUM(unit_price)
FROM track
GROUP BY album_id;




RATIONALE
Common mistakes include- forgetting the "AS", not doing a select
statement, and not including the FROM clause.

CONCEPT
 VIEW to Provide a Subset

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3 


In each milestone, you may want or need to use the database
and query tool to answer some of the questions. We suggest you
open the tool in another browser tab while you are working on
this assessment.

https://postgres.sophia.org/

, Which of the following queries will use a subquery to find all of
theUNIT
rows in2the
—track
MILESTONE
table that has2a unit_price of 0.99 and has
the length of the song in milliseconds that is longer than the
AVG track length of all tracks in the album_id between 5 and 20/25
10?



SELECT *
FROM TRACK
WHERE milliseconds >
SELECT AVG(milliseconds)
 FROM track
WHERE album_id BETWEEN 5
AND 10
AND unit_price = 0.99;



SELECT *
FROM TRACK
WHERE milliseconds >
(SELECT AVG(milliseconds)
  FROM track
WHERE album_id BETWEEN 5
AND 10)
AND unit_price = 0.99;



SELECT AVG(milliseconds)
FROM TRACK
WHERE milliseconds >
(SELECT *
 FROM track
WHERE album_id BETWEEN 5
AND 10)
AND unit_price = 0.99;



SELECT *
FROM TRACK
WHERE milliseconds >