01
DBMS foundations and architecture
08
Relational model, keys and constraints
Interview questions
DBMS interview questions
Practise explaining databases and SQL clearly, like you would in a real interview.
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02
DBMS foundations and architecture
How is a DBMS better than storing data directly in files?
03
DBMS foundations and architecture
What is the difference between a database schema and a database instance?
04
DBMS foundations and architecture
What does the three-schema architecture try to achieve?
05
DBMS foundations and architecture
What makes a relational DBMS different from a general DBMS?
06
Relational model, keys and constraints
What do relation, tuple, attribute, and domain mean in the relational model?
07
Relational model, keys and constraints
How do a super key, candidate key, and primary key differ?
09
Relational model, keys and constraints
What does a foreign key guarantee?
10
Relational model, keys and constraints
Why should important validation also exist as database constraints?
11
Relational model, keys and constraints
Why can NULL produce unexpected SQL results?
12
ER modelling and schema design
What are entities, attributes, and relationships in an ER model?
13
ER modelling and schema design
What is the difference between cardinality and participation?
14
ER modelling and schema design
What is a weak entity, and how would you model it?
15
ER modelling and schema design
How do you represent a many-to-many relationship in a relational database?
16
ER modelling and schema design
When would you choose a surrogate key over a natural key?
17
SQL filtering, grouping and aggregation
What is the difference between WHERE and HAVING?
18
SQL filtering, grouping and aggregation
What rule do you follow when writing a GROUP BY query?
19
SQL filtering, grouping and aggregation
How do COUNT(*) and COUNT(column) differ?
20
SQL filtering, grouping and aggregation
How would you find duplicate email addresses in a users table?
21
SQL filtering, grouping and aggregation
How would you find the second-highest distinct salary?
22
SQL filtering, grouping and aggregation
How would you count completed and pending orders in one query?
23
SQL filtering, grouping and aggregation
What is the difference between DELETE, TRUNCATE, and DROP?
24
Joins, subqueries, views and CTEs
How do INNER, LEFT, RIGHT, and FULL joins differ?
25
Joins, subqueries, views and CTEs
Why can moving a condition from ON to WHERE change a LEFT JOIN result?
26
Joins, subqueries, views and CTEs
How would you show each employee with their manager's name?
27
Joins, subqueries, views and CTEs
What is a correlated subquery?
28
Joins, subqueries, views and CTEs
When would you use EXISTS instead of IN?
29
Joins, subqueries, views and CTEs
How would you find customers who have never placed an order?
30
Joins, subqueries, views and CTEs
How would you find employees earning above their department average?
31
Joins, subqueries, views and CTEs
How do a CTE, a view, and a materialized view differ?
32
Functional dependencies and normalization
What is a functional dependency?
33
Functional dependencies and normalization
What problems does normalization try to prevent?
34
Functional dependencies and normalization
What does First Normal Form require?
35
Functional dependencies and normalization
When does a table violate Second Normal Form?
36
Functional dependencies and normalization
How would you explain the difference between 3NF and BCNF?
37
Functional dependencies and normalization
What do lossless join and dependency preservation mean?
38
Functional dependencies and normalization
When would you intentionally denormalize a schema?
39
Transactions, ACID and isolation levels
What is a database transaction?
40
Transactions, ACID and isolation levels
Can you explain the ACID properties with practical meaning?
41
Transactions, ACID and isolation levels
What is the difference between atomicity and durability?
42
Transactions, ACID and isolation levels
What are dirty reads, non-repeatable reads, and phantom reads?
43
Transactions, ACID and isolation levels
How do you choose a transaction isolation level?
44
Transactions, ACID and isolation levels
What is MVCC, and does it remove the need for locks?
45
Transactions, ACID and isolation levels
How do you decide where a transaction should begin and end?
46
Concurrency, locking and deadlocks
What is the difference between shared and exclusive locks?
47
Concurrency, locking and deadlocks
What is two-phase locking, and what does strict 2PL add?
48
Concurrency, locking and deadlocks
How does a database deadlock happen, and how should an application handle it?
49
Concurrency, locking and deadlocks
When would you use optimistic versus pessimistic locking?
50
Concurrency, locking and deadlocks
How would you prevent two requests from overwriting each other's update?
51
Indexing, storage and query optimization
What is an index, and why not index every column?
52
Indexing, storage and query optimization
When is a B-tree index more useful than a hash index?
53
Indexing, storage and query optimization
What is the difference between clustered and nonclustered indexes?
54
Indexing, storage and query optimization
Why does column order matter in a composite index?
55
Indexing, storage and query optimization
Why might the optimizer ignore an available index?
56
Indexing, storage and query optimization
How do you use an execution plan to improve a query?
57
Recovery and practical scenarios
A query became slow in production. How would you investigate it?
58
Recovery and practical scenarios
An order was created but inventory was not reserved. How would you prevent that state?
59
Recovery and practical scenarios
How do write-ahead logging and checkpoints help crash recovery?
60
Recovery and practical scenarios