PostgreSQL

PostgreSQL is a powerful and advanced relational database management system that utilizes SQL commands for defining, modifying and deleting database structures such as tables, indexes and schemas. Two key features of PostgreSQL are auto-generating values for columns and using primary and foreign keys to maintain unique identifiers and maintain referential integrity between tables.

Auto Generated values in PostgreSQL can be achieved using SERIAL or GENERATED AS IDENTITY. For instance, a column can be declared SERIAL to automatically generate an ID for each new row inserted. The alternative approach is to utilize an INT column and use GENERATED AS IDENTITY to automatically assign a unique identifier.

Primary keys are a crucial aspect of PostgreSQL, ensuring that each row in a table can be uniquely identified by a column or group of columns. These values must be both unique and not null. Primary keys can also be defined across multiple columns, creating composite primary keys using the syntax similar to unique constraints.

Foreign keys, on the other hand, maintain referential integrity between two related tables by ensuring that the values in a column (or group of columns) match the values present in another table. This linkage prevents any data inconsistencies and maintains data integrity.

When it comes to table and view structures in SQL, both serve to organize and access data within a database. Tables store actual data in rows and columns, while views are virtual tables created using an SQL query that extract data from one or more existing tables. Tables are permanent database objects, whereas views are transient and dependent on the underlying tables. Tables can be manipulated using DDL, DML, and DQL commands, while views are primarily used for SELECT operations.

The commands used in SQL can be categorized into five main types: DDL (Data Definition Language), DQL (Data Query Language), DML (Data Manipulation Language), DCL (Data Control Language), and TCL (Transaction Control Language). DDL commands define, modify, or delete database structures, DQL commands fetch data, DML commands manipulate data, DCL commands control access, and TCL commands manage transactions and ensure data integrity.

In SQL, data can be deleted, truncated, or dropped using specific commands, each with distinct functionalities. While DELETE removes specific rows based on conditions, TRUNCATE removes all rows from a table, and DROP removes the entire table.

SQL and NoSQL are two distinct database management systems. SQL is a relational database that stores data in tables with rows and columns, ensuring a structured approach. NoSQL, on the other hand, is a non-relational database that can store data in various formats such as documents, key-value pairs, or graphs. SQL is versatile and powerful for complex queries, while NoSQL offers flexibility for diverse data storage requirements.

PostgreSQL and MySQL are prominent examples of SQL databases, while MongoDB and Redis are popular NoSQL databases.

Finally, functions and stored procedures serve similar purposes in PostgreSQL, but they possess distinct characteristics. Functions are used to perform specific tasks or sequences of operations and can optionally return a value, whereas stored procedures can also be invoked within a SELECT statement but do not necessarily return a value.

Constraints are used to maintain data accuracy and integrity, with NOT NULL ensuring non-null values, UNIQUE enforcing unique values, PRIMARY KEY combining both NOT NULL and UNIQUE, FOREIGN KEY establishing relationships between tables, CHECK enforcing specific conditions, and DEFAULT setting default values for columns.