Relational Database

What is Normalization in Database?

Normalization is the process of organizing data in a database to reduce redundancy, avoid anomalies, and improve data integrity.

What are ACID Properties in DBMS?

ACID stands for Atomicity, Consistency, Isolation, and Durability — the four guarantees a database transaction must satisfy so that data stays correct even und…

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 an Index in a Database?

A database index is a data structure that speeds up read queries by letting the database find rows without scanning the entire table, at the cost of extra stor…

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.

Difference Between Primary Key and Foreign Key

A primary key uniquely identifies each row in a table and cannot be NULL, while a foreign key is a column that references the primary key of another table to l…

Difference Between DELETE, TRUNCATE and DROP

DELETE removes selected rows and can be rolled back, TRUNCATE quickly removes all rows but keeps the table structure, and DROP removes the entire table includi…

What is a View in SQL?

A view is a virtual table defined by a stored SQL query; it holds no data of its own but presents the result of that query as if it were a table whenever you s…

What is a Transaction in a Database?

A transaction is a sequence of one or more database operations that executes as a single, indivisible unit of work — either every operation succeeds and commit…

What is Database Sharding?

Database sharding is a horizontal partitioning technique that splits a large dataset across multiple independent database servers (shards), where each shard ho…

Clustered vs Non-Clustered Index: What is the Difference?

A clustered index determines the physical order in which table rows are stored on disk, while a non-clustered index is a separate structure that stores pointer…

What is a Stored Procedure in SQL?

A stored procedure is a precompiled, named block of SQL statements saved inside the database that can be executed repeatedly with a single call, optionally acc…

What is Database Replication?

Database replication is the process of continuously copying data from one database server (the primary) to one or more other servers (replicas), so multiple co…

Inner Join vs Outer Join

An INNER JOIN returns only the rows that have matching values in both tables, while an OUTER JOIN (LEFT, RIGHT, or FULL) returns matched rows plus unmatched ro…

What is a Composite Key?

A composite key is a primary key made up of two or more columns that, together, uniquely identify a row, even though no single column among them is unique on i…

HAVING vs WHERE Clause

WHERE filters individual rows before any grouping or aggregation happens, while HAVING filters groups after GROUP BY has aggregated them, so HAVING is the only…

What is a Cursor in SQL?

A cursor is a database object that lets a program process a query result set one row at a time, instead of the usual set-based operation that acts on all match…

CHAR vs VARCHAR

CHAR is a fixed-length string type that always stores and pads to its declared length, while VARCHAR is a variable-length type that stores only the actual char…

What is the Difference Between GROUP BY and ORDER BY?

GROUP BY aggregates rows that share a common value into summary rows, while ORDER BY simply sorts the result set without changing how many rows are returned.

What is Referential Integrity?

Referential integrity is a database rule ensuring that a foreign key value in one table always matches an existing primary key value in the referenced table, p…

How Does a B-Tree Index Work Internally?

A B-tree index is a balanced, sorted tree of fixed-size nodes where every leaf sits at the same depth, letting the database find any key in O(log n) disk reads…

Hash Index vs B-Tree Index: What is the Difference?

A hash index maps each key to a bucket via a hash function, giving O(1) average-case exact-match lookups but no support for range queries or ordering, while a…

What is a Covering Index in SQL?

A covering index is an index that includes every column a query needs — both the filter/sort columns and the selected columns — so the database engine can answ…

What is a Partial Index and When Should You Use One?

A partial index is an index built over only the subset of rows that satisfy a WHERE condition, rather than every row in the table, which keeps it smaller, fast…