SQL Query

Question 2

What is querying in SQL?

Answer 2

The act of retrieving specific data from a database using SELECT-based commands.

Question 3

What is the full structure of an SQL query?

Answer 3

SELECT … FROM … WHERE … GROUP BY … HAVING … ORDER BY … LIMIT …

Question 4

Which clause is executed last in SQL?

Answer 4

SELECT.

Question 5

Why is SELECT executed last?

Answer 5

Because it operates on the table that has already been filtered, grouped, and sorted by previous clauses.

Question 6

What does the SELECT clause do?

Answer 6

It retrieves specific columns, expressions, or function outputs from the processed table.

Question 7

What does DISTINCT do in SELECT?

Answer 7

Removes duplicate results from the returned set.

Question 8

What does AS do in SELECT?

Answer 8

Assigns a temporary alias to a column or expression for readability.

Question 9

What is the purpose of the FROM clause?

Answer 9

It tells SQL which table(s) to retrieve data from.

Question 10

Why is the FROM clause necessary even when the table name is mentioned?

Answer 10

Because SQL needs an explicit instruction to locate data sources.

Question 11

What does the WHERE clause do?

Answer 11

Filters rows before grouping, keeping only rows where conditions are true.

Question 12

Give examples of condition types usable in WHERE.

Answer 12

Comparison operators (> < =), logic (AND, OR), IN, BETWEEN, IS NULL.

Question 13

What does the GROUP BY clause do?

Answer 13

It groups rows based on matching values in one or more columns.

Question 14

What happens if you GROUP BY multiple columns?

Answer 14

SQL groups rows that match on all specified columns.

Question 15

What does the HAVING clause do?

Answer 15

Filters groups after GROUP BY has created them.

Question 16

Can you use HAVING without GROUP BY?

Answer 16

Yes, it then treats the result set as one big group.

Question 17

Why can’t WHERE be used after GROUP BY?

Answer 17

Because WHERE works on individual rows, not groups.

Question 18

What does ORDER BY do?

Answer 18

Sorts the result rows based on column values.

Question 19

What is the default sort order in ORDER BY?

Answer 19

Ascending (ASC).

Question 20

How do you sort descending?

Answer 20

Use DESC after the column name.

Question 21

What happens when sorting by multiple columns?

Answer 21

SQL sorts by the first column, then breaks ties using the next.

Question 22

What does the LIMIT clause do?

Answer 22

Restricts the number of rows returned.

Question 23

How can you skip a number of rows before returning results?

Answer 23

Use OFFSET with LIMIT: LIMIT offset, count

Question 24

What are aggregate functions used for?

Answer 24

To summarize or perform operations on groups of rows.

Question 25

Give 5 aggregate functions.

Answer 25

COUNT(), SUM(), AVG(), MIN(), MAX()

Question 26

If you want to find employees in 'Sales', what clause do you use?

Answer 26

WHERE department = 'Sales'

Question 27

If you want to see departments with total salaries over $100k?

Answer 27

Use GROUP BY department and HAVING SUM(salary) > 100000

Question 28

If you want the top 3 oldest employees?

Answer 28

ORDER BY age DESC LIMIT 3

Question 29

Spot the mistake: 'SELECT * employees;'

Answer 29

Missing FROM clause: should be SELECT * FROM employees;

Question 30

Spot the mistake: 'ORDER name BY ASC;'

Answer 30

Correct form is: ORDER BY name ASC;

Question 31

List the execution order of SQL SELECT query parts.

Answer 31

FROM → WHERE → GROUP BY → HAVING → ORDER BY → SELECT → LIMIT

Question 32

Explain the difference between WHERE and HAVING.

Answer 32

WHERE filters rows before grouping; HAVING filters after groups are formed.

Question 33

Describe the role of GROUP BY in data summarization.

Answer 33

It segments data by categories so aggregate functions can operate on each group.

Question 34

If you forget GROUP BY when using HAVING, what happens?

Answer 34

SQL treats the entire table as one group.

Question 35

If you omit WHERE and HAVING, what filtering is applied?

Answer 35

None. All rows (and groups) are included.