Category: SQL Faqs

SQL databases are characterized by their use of structured tables and strict adherence to a predefined schema, making them ideal for managing structured data with a strong focus on data consistency and transaction support. In contrast, NoSQL databases are non-relational and excel in handling unstructured or semi-structured data, frequently employed for scalable, distributed, and adaptable data storage…

A database is a systematically organized collection of data arranged into tables composed of rows and columns. The primary purpose of databases is to efficiently store, manage, and retrieve data.

Often referred to as a unique constraint, a unique key guarantees that every value in a column (or a combination of columns) remains distinct and cannot be replicated within a table. In contrast to a primary key, a table has the flexibility to incorporate multiple unique keys.

A NULL value in SQL represents the absence of data in a column. It is not the same as an empty string or zero; it signifies that the data is missing or unknown. NULL values can be used in columns with optional data or when the actual data is unavailable.

A JOIN operation merges information from two or more tables by utilizing a common column that links them together. Various types of JOINs exist, like INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN. These JOIN variations dictate the manner in which data from the involved tables is paired and retrieved.

The DELETE command is used by professionals to remove particular rows from a table based on a condition, allowing you to selectively delete records. TRUNCATE, on the other hand, removes all rows from a table without specifying conditions. TRUNCATE is faster and uses fewer system resources than DELETE but does not log individual row deletions.

It is a field in one table referencing the primary key in another. It establishes a relationship between the two tables, ensuring data consistency and enabling data retrieval across tables.

It is a unique identifier for each record in a table. It ensures that each row in the table has a distinct and non-null value in the primary key column. Primary keys enforce data integrity and create relationships between tables.

SQL means Structured Query Language and is used to communicate with relational databases. It proposes a standardized way to interact with databases, allowing users to perform various operations on the data, including retrieval, insertion, updating, and deletion.