Data Modeling

Difference Between SQL and NoSQL Databases

SQL databases are relational, store data in structured tables with a fixed schema, and use SQL for querying; NoSQL databases are non-relational, store data in…

What is a JOIN in SQL?

A SQL JOIN combines rows from two or more tables based on a related column, letting you query normalized data as if it were a single table.

What is a Self-Join and When Would You Use One?

A self-join is a regular join where a table is joined with itself, typically by giving the table two different aliases so rows can be compared against other ro…

What is a CROSS JOIN and When is it Useful?

A CROSS JOIN produces the Cartesian product of two tables, pairing every row from the first table with every row from the second table, with no join condition…

What is the Document Database Model?

A document database stores each record as a self-contained, semi-structured document, typically JSON or BSON, where related fields and nested data live togethe…

What is a Column-Family Database Model?

A column-family database groups related columns into named families and stores each row's data physically by column family rather than by row, so queries touch…

What is the Graph Database Model?

A graph database stores data as nodes (entities) and edges (relationships between them), both of which can carry properties, and it is optimized to traverse re…

What is a Key-Value Store and When Should You Use One?

A key-value store is the simplest NoSQL model: every item is an opaque value retrieved by a unique key, with no required schema and no built-in support for que…

Wide-Column Store vs Relational Database: What is the Difference?

A wide-column store lets each row hold millions of dynamically named, sparse columns grouped by family and distributed by row key across many nodes, while a re…

How Do You Design Document Schemas in MongoDB?

MongoDB document schema design means choosing, for each relationship in your data, whether to embed related data inside a single document or reference it from…

What Are the Basics of Cassandra Data Modeling?

Cassandra data modeling means designing tables around the exact queries your application will run, since Cassandra has no joins and limited ad-hoc filtering, s…

What Are the Basics of Graph Queries in Neo4j?

Neo4j stores data as nodes (entities) and relationships (typed, directed connections between them), and Cypher, its query language, lets you match patterns of…

How Do You Design a Good Partition Key in DynamoDB?

A good DynamoDB partition key spreads items as evenly as possible across the table's underlying partitions by having high cardinality and uniform access freque…

How Do You Choose Numeric Data Type Precision in a Database?

Choosing numeric precision means matching a column’s storage size and rounding behavior to the exact range and accuracy the data needs — using fixed-point type…

How Should Databases Handle Dates, Times, and Time Zones?

The safest approach is to store every timestamp in UTC using a timezone-aware type, and convert to a user's local time zone only at the presentation layer, so…

When Should You Use a JSON Column Type in a Relational Database?

A JSON column makes sense for semi-structured, sparse, or frequently changing attributes that do not fit cleanly into fixed columns — such as user preferences,…

ENUM Type vs Lookup Table: Which Should You Use?

An ENUM type is best for a small, genuinely fixed set of values that almost never changes and needs compact, fast storage, while a lookup table (a separate ref…

How Should You Decide Which Columns Get a NOT NULL Constraint?

A NOT NULL constraint should be applied to any column whose absence would make a row meaningless or would break downstream logic, such as identifiers, foreign…

Star Schema vs Snowflake Schema: What is the Difference?

A star schema keeps each dimension table fully denormalized in one flat table around a central fact table, while a snowflake schema further normalizes those di…

What Are the Basics of Entity-Relationship (ER) Modeling?

Entity-relationship modeling represents a database's structure using entities (things like Customer or Order), attributes (properties of those entities), and r…

What Are Fact and Dimension Tables in a Data Warehouse?

A fact table stores the measurable, numeric events of a business process — like sales amount or quantity sold — along with foreign keys to related dimensions,…

What Are Time-Series Databases and When Should You Use One?

A time-series database is a storage engine purpose-built for data points indexed by time, optimizing for high-volume append-only writes, time-range queries, an…

What Are TimescaleDB Hypertables and How Do They Work?

A TimescaleDB hypertable is a PostgreSQL table that is automatically partitioned behind the scenes into many smaller physical tables called chunks, typically s…

How Does the InfluxDB Data Model Work?

InfluxDB organizes data around measurements, which act like tables, and each data point within a measurement is defined by a timestamp, a set of indexed tags (…