Oracle SQL 12 c

SQL stands for Structured Query Language , and it is used to communicate with the Database. This is a standard language used to perform tasks such as retrieval, updation, insertion and deletion of data from a database.Standard SQL Commands are Select.

Database is nothing but an organized form of data for easy access, storing, retrieval and managing of data. This is also known as structured form of data which can be accessed in many ways.Example: School Management Database, Bank Management Database.

A primary key is a combination of fields which uniquely specify a row. This is a special kind of unique key, and it has implicit NO

A Unique key constraint uniquely identified each record in the database. This provides uniqueness for the column or set of columns.A Primary key constraint has automatic unique constraint defined on it. But not, in the case of Unique Key.There can be many unique constraint defined per table, but only one Primary key constraint defined per table.

A foreign key is one table which can be related to the primary key of another table. Relationship needs to be created between two tables by referencing foreign key with the primary key of another table.

This is a keyword used to query data from more tables based on the relationship between the fields of the tables. Keys play a major role when JOINs are used.

A DB query is a code written in order to get the information back from the database. Query can be designed in such a way that it matched with our expectation of the result set. Simply, a question to the Database.

A subquery is a query within another query. The outer query is called as main query, and inner query is called subquery. SubQuery is always executed first, and the result of subquery is passed on to the main query.