Multi-Table Relational SQL :Using Databases with Python (Python for Everybody Specialization) Answers 2025

Question 1

What is the primary added value of relational databases over flat files?

✅ Ability to scan large amounts of data quickly
❌ Ability to convert to HTML
❌ Execute JavaScript
❌ Send across network
❌ Execute Python code

Explanation:
Relational databases allow fast searching, indexing, and joining of large datasets — which flat files cannot do efficiently.

Question 2

What is the purpose of a primary key?

✅ To look up a particular row in a table very quickly
❌ To track duplicates
❌ To point to another table
❌ To look up based on a string

Explanation:
A primary key uniquely identifies a row and allows quick access within a table.

Question 3

Which of the following is NOT a good rule to follow when developing a database model?

✅ Use a person’s email address as their primary key
❌ Model each “object” as one or more tables
❌ Never repeat string data
❌ Use integers as primary keys

Explanation:
Emails can change — they are not reliable identifiers. Always use integer-based primary keys for consistency.

Question 4

If a user interface has repeated strings on one column, how should we model it in a database?

✅ Make a table that maps the strings in the column to numbers and then use those numbers in the column
❌ Put NULLs
❌ Use row numbers
❌ Encode as JSON

Explanation:
This is normalization — repeated data should be moved into a separate lookup table and linked using foreign keys.

Question 5

Which column label is used by the “outside world” to look up a particular row?

✅ Logical key
❌ Local key
❌ Remote key
❌ Foreign key
❌ Primary key

Explanation:
A logical key is meaningful outside the database (like email or username).
A primary key is internal and system-generated.

Question 6

What is the label for a column used to point to a row in another table?

✅ Foreign key
❌ Logical key
❌ Local key
❌ Remote key
❌ Primary key

Explanation:
A foreign key links rows in one table to primary keys in another table.

Question 7

What SQLite keyword is added to primary keys to have the database auto-generate values?

✅ AUTOINCREMENT
❌ INSERT_AUTO_PROVIDE
❌ AUTO_INCREMENT
❌ ASSERT_UNIQUE

Explanation:
In SQLite, AUTOINCREMENT tells the database to automatically generate an integer ID for each new row.

Question 8

What SQL keyword reconnects rows with foreign keys to the referenced data?

✅ JOIN
❌ APPEND
❌ COUNT
❌ CONNECT
❌ CONSTRAINT

Explanation:
JOIN merges data from multiple tables based on related columns (usually foreign key relationships).

Question 9

What happens when you JOIN two tables without an ON clause?

✅ The number of rows = rows in table 1 × rows in table 2
❌ You get NULLs
❌ You get no rows
❌ Syntax error
❌ Only matching rows

Explanation:
Without an ON clause, SQL performs a Cartesian product — every row in table A is paired with every row in table B.

Question 10

How do you distinguish identical column names when joining multiple tables?

✅ tablename.columnname
❌ tablename->columnname
❌ tablename[‘columnname’]
❌ tablename/columnname

Explanation:
Use dot notation (table.column) to specify which table a column belongs to in a multi-table query.

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