TOC Database Management & SQL 2

Question 1

Which SQL JOIN type returns only rows where there is a match in BOTH tables?

Accepted Answer

INNER JOIN

Answer

INNER JOIN returns only the rows that have matching values in both joined tables.

Question 2

In SQL, which aggregate function returns the number of non-NULL values in a column?

Accepted Answer

COUNT()

Answer

COUNT(column_name) counts non-NULL values, while COUNT(*) counts all rows including NULLs.

Question 3

Which clause is used to filter results AFTER a GROUP BY aggregation?

Accepted Answer

HAVING

Answer

HAVING filters grouped results after aggregation, whereas WHERE filters rows before grouping.

Question 4

A talent database query needs to list all employees and their managers, including employees with no manager. Which JOIN is most appropriate?

Accepted Answer

LEFT JOIN

Answer

LEFT JOIN returns all rows from the left (employees) table even when no matching row exists in the right (managers) table.

Question 5

What does the SQL keyword DISTINCT do when used in a SELECT statement?

Accepted Answer

Removes duplicate rows from results

Answer

DISTINCT eliminates duplicate rows so each unique combination of selected column values appears only once.

(TOC) Talent Optimization Consultant Practice Test