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SQL Queries | SELECT DISTINCT + COUNT( ) Function

Consider a Employees data set contains following tables:
Departments - dept_no, dept_name
Dep_emp - emp_no, dept_no, from_date, to_date
Dep_manager - emp_no, dept_no, from_date, to_date
Employees - emp_no, birth_date, first_name, last_name, gender, hire_date
Salaries - emp_no, salary, from_date, to_date
Titles - emp_no, titles, from_date, to_date

SELECT DISTINCT is used to retrieve unique values from a specified column or combination of columns in a result set. It is commonly used in the SELECT statement to filter out duplicate rows and return only the distinct values.

DDL – Data Definition Language
DML – Data Manipulation Language
DCL – Data Control Language
TCL – Transaction Control Language

Data Definition Language: Used to create, modify & delete database objects such as tables, views, indexes & constraints.

Data Manipulation Language: Used to SELECT, insert, update, delete & retrieve data from a database table.

Data Control Language. Used to manage access control and security of a data base. Commands like GRANT, REVOKE.

Transaction Control Language. Used to manage transactions in a data base. Commands like COMMIT, ROLL BACK.

These subsets of SQL allow users to perform different types of operations on a database and provide a powerful set of tools for managing and manipulating data.

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