DA SQL and Database Querying 3

Question 1

What is a primary key in a relational database?

Accepted Answer

A column that uniquely identifies each row

Answer

The first column created in a table

Answer

A foreign reference to another table

Answer

A column that allows NULL values

Question 2

Which SQL clause limits the number of rows returned by a query?

Accepted Answer

All of the above (syntax varies by database)

Answer

TOP

Answer

LIMIT

Answer

ROWNUM

Question 3

What does the COALESCE function do in SQL?

Accepted Answer

Returns the first non-NULL value in a list

Answer

Converts data types

Answer

Combines two strings

Answer

Rounds a numeric value

Question 4

What is a CTE (Common Table Expression) in SQL?

Accepted Answer

A temporary named result set defined within a WITH clause

Answer

A permanent stored procedure

Answer

A type of database index

Answer

A cross-table join method

Question 5

Which SQL aggregate function returns the highest value in a column?

Accepted Answer

MAX()

Answer

TOP()

Answer

HIGHEST()

Answer

UPPER()

Question 6

What is the difference between DELETE and TRUNCATE in SQL?

Accepted Answer

DELETE can include a WHERE clause; TRUNCATE removes all rows without logging individual deletions

Answer

DELETE removes the table; TRUNCATE removes rows

Answer

TRUNCATE supports rollback; DELETE does not

Answer

There is no functional difference