Interview Q&A

Extract the data from the source database using export tools or direct queries.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Store migration scripts in version control (e.g., Git) and ensure that each change is applied in a sequential, ordered fashion.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Each tenant has its schema in the same database. The schema contains the same tables but is isolated per tenant. Pros: Better data isolation compared to the first approach. Cons: More complex to manage schema changes across tenants.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• A pattern used when two entities are related in a way where both can have

multiple associations with each other.

• Example: A Student can be enrolled in many Courses, and a Course can

have many Students. This would typically be modeled using a junction table

like Student_Course.

Answer: Monitor CPU, memory usage, disk I/O, and network latency using tools like Prometheus, Grafana, or cloud-specific monitoring tools like AWS CloudWatch or Azure Monitor.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Partition large tables into smaller, more manageable subsets, which can make queries faster. Example: Split a sales table by year to avoid scanning years of data in a single query.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• Two or more databases act as both masters and slaves, allowing for both

read and write operations on any node.

• Advantages: High availability and load balancing for both reads and writes.
• Disadvantages: Potential for data conflicts when writes happen

simultaneously on multiple nodes.

Answer: Use cron jobs to automate pg_dump commands. Example (Linux): 0 3 * * * pg_dump -U postgres mydatabase > /path/to/backup/mydatabase_$(date +\%Y\%m\%d).sql Use pgBackRest or Barman for more advanced backup automation.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• A differential backup includes all the changes made since the last full backup.

It does not depend on other differential backups.

• Advantages: Smaller than a full backup, and quicker to take compared to full

backups.

• Disadvantages: Can become larger over time as more changes accumulate

between full backups.

• Example: If the last full backup was taken on Monday, a differential backup

taken on Wednesday would include all changes since Monday.

Answer: ccess-controlled locations, ideally offsite or in the cloud (e.g., AWS S3, Azure Blob Storage). Use encrypted cloud storage options.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: A Customer can have multiple Orders. An Order can contain multiple Products (many-to-many relationship). A Product can belong to multiple Categories. Payments are linked to Orders.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

use foreign keys to link them.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: on the primary key. Remove partial dependencies (when a non-key attribute depends on part of a composite key).

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

query.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

usage.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: WHERE, JOIN, ORDER BY, and GROUP BY clauses to choose the most appropriate index.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

frequently.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

BY are faster.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• Structured Data: SQL is best suited for structured data where relationships between

data are important.

• ACID Compliance: SQL databases generally support ACID (Atomicity, Consistency,

Isolation, Durability) properties, making them ideal for applications where data

integrity is crucial, such as banking systems.

• Complex Queries: SQL databases provide powerful query capabilities with joins,

subqueries, and aggregations.

• Maturity and Ecosystem: SQL databases have been around for decades, offering a

robust set of features, tools, and community support.

vailability will fail during network partitions.

• CP (Consistency and Partition Tolerance): Systems that prioritize consistency and

partition tolerance may not be available during network issues.

• AP (Availability and Partition Tolerance): Systems that prioritize availability and

partition tolerance may return stale data.

nd cache usage to monitor the internal database performance.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

nother non-key attribute.

For example:

• Original Table:

Employee_ID Employee_Nam

Department Department_Manager

1 Alice HR John

2 Bob IT Sarah

• ● 1NF: Remove repeating groups and ensure atomic values.
• 2NF: Remove partial dependencies. In this case, split into separate tables for

employees and departments.

• 3NF: Remove transitive dependencies. The Department_Manager is a dependency

on Department, not directly on Employee, so it should be moved to a separate table

for Departments.

visible to other transactions.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: matched rows from the left table. If there’s no match, NULL is returned for the left table. Use case: When you want all records from the right table.

What interviewers expect

• A clear definition tied to SQL in SQL & Databases projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production SQL & Databases application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in SQL & Databases architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Trade-offs:

• CA (Consistency and Availability): Systems that prioritize consistency and

availability will fail during network partitions.

• CP (Consistency and Partition Tolerance): Systems that prioritize consistency and

partition tolerance may not be available during network issues.

• AP (Availability and Partition Tolerance): Systems that prioritize availability and

partition tolerance may return stale data.