Essential SQL Interview Questions

Question 1 of 10

1. Question

There is a table which contains two columns: Student and Marks

Which query would you use to find all the students, whose marks are greater than average marks?

SELECT Student, Marks FROM Grades WHERE Marks > AVG(Marks)
SELECT Student, Marks FROM Grades GROUP BY Student HAVING Marks > AVG (Marks)
SELECT Student, Marks FROM Grades WHERE Marks > (SELECT AVG(Marks) from Grades)
SELECT Student, Marks FROM Grades ORDER BY Marks OFFSET AVG(MARKS) FETCH NEXT

Question 2 of 10

2. Question

An inner join is used to return which of the following?

Rows in one table but not another.
Columns from two tables whose rows match a join criteria.
All columns from all tables.
Only rows whose primary keys match.

Question 3 of 10

3. Question

Which of the following operators is allowed in a join condition?

= (equals)
> (greater than)
< (less than)
<> (not equals)
All of the Above
None of the Above

Question 4 of 10

4. Question

Given the following example:
SELECT A.Name, B.Age FROM Person A INNER JOIN Person B ON A.ID = B.ID

What most accurately describes what kind of join it is?

Self Join
Cross Join
Inner Join
Outer Join
Cross Join
Equi Join

Question 5 of 10

5. Question

Given the following statement what do you think is incorrect?

SELECT DepartmentName, (SELECT name FROM Employee) FROM Department

The subquery column doesn’t have an alias.
The subquery most likely returns more than one value.
The subquery table isn’t correlated with the outer query table.
There are no numeric values in the subquery.

Question 6 of 10

6. Question

What is the main purpose of the primary key?

To sort the table by the most used columns.
To limit the number of rows you can view in a query.
To uniquely identify each row within the table.
To tie each row to the previous row in the database.
All of the Above.
None of the Above.

Question 7 of 10

7. Question

A database that is in first normal form follow all these rules except:

Information is stored in a relational table.
The table has a primary key.
The repeating columns are consistently named.
Each column contains atomic values.

Question 8 of 10

8. Question

Which statement is not true about relational database tables?

A table can have only one primary key.
A table can have only one foreign key.
A table must have at least one row to be defined.
Each column name is unique.

Question 9 of 10

9. Question

What is the difference between UNION and UNION ALL?

The main difference is that UNION ALL returns all rows from the first query and unique rows from the second.
The difference lies in the fact that UNION is used to find rows not in common to both queries, whereas; UNION ALL finds all rows common.
UNION returns every row from both queries and UNION ALL returns all unique rows.
UNION ALL returns every row from both queries and UNION just the unique rows.

Question 10 of 10

10. Question

Which Query best finds all Employee records containing the word “Joe”, regardless of capitalization (e.g. JOE, Joe, or joe)?

SELECT ID, Name FROM Employee WHERE FirstName in (‘Joe’,’JOE’,’joe’)
SELECT ID, Name FROM Employee WHERE UPPER(FirstName) = ’JOE’
SELECT ID, Name FROM Employee WHERE FirstName like ’joe’

Essential SQL Interview Questions

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