Relational Model and SQL: 10 practice questions

Question 1 of 10

In a SELECT query, which part states the values or expressions that appear in the output?

1. AThe statement terminator
2. BThe WHERE clause
3. CThe select list
4. DThe FROM clause

Question 2 of 10

A table already has three unique constraints. How many primary keys may it also declare?

1. AExactly three primary keys
2. BOne for every unique constraint
3. CAt most one primary key
4. DNone because unique constraints already exist

Question 3 of 10

Which referenced columns give a foreign key one row to match?

1. AColumns covered by a primary key or suitable unique constraint
2. BEvery column in the referenced table
3. CAny column used in a WHERE clause
4. DAny column that contains no nulls and is indexed in both tables

Question 4 of 10

What does SELECT 2 + 3 produce when it has no FROM clause?

1. AA one-column result containing 5
2. BAn empty result because there are no input rows
3. CA stored value added to the database
4. DA syntax error because every SELECT needs a table

Question 5 of 10

A customer table has unique, non-null email and customer_number columns. Other tables need one stable declared identity, while email must still reject duplicates. Which design fits?

1. AUse customer_number as the primary key and keep a unique constraint on email
2. BKeep only NOT NULL on both columns
3. CReference email without a key constraint
4. DDeclare both columns as separate primary keys because each is unique in its own column

Question 6 of 10

A report must calculate quantity * unit_price for each returned row without changing which rows are kept. Where does the calculation belong?

1. AIn the select list as a value expression
2. BIn WHERE as the row condition
3. CIn FROM as a table name
4. DAfter the semicolon as part of a second clause

Question 7 of 10

Which two properties make primary-key values reliable for identifying rows?

1. AThey are text and sorted
2. BThey are copied into every related table
3. CThey are generated by the database
4. DThey are unique and never null

Question 8 of 10

An order has a non-null customer_id that matches no row in the referenced customer key. What does the foreign-key rule require?

1. ACreate a customer row automatically
2. BChange the unmatched value to zero
3. CAccept the order because constraints do not apply across separate tables
4. DReject the order until the value matches a referenced row

Question 9 of 10

Which statement distinguishes a value expression from a table expression?

1. ABoth always return a complete table
2. BA value expression filters rows, while a table expression only renames columns
3. CA value expression returns one scalar; a table expression produces rows and columns
4. DA value expression is a full statement, while a table expression is a semicolon

Question 10 of 10

Consider SELECT price * quantity AS total FROM order_items WHERE quantity > 1;. Which description labels its parts correctly?

1. AFROM is the statement, SELECT is a table, and the semicolon is the result set
2. BEvery word is a separate statement because SQL is token based
3. CWHERE is an expression, price is a clause, and order_items is the statement
4. DIt is the statement with clauses and expressions; its returned rows are the result set