SELECT DISTINCT COUNT(Department_Id) FROM Employees;

SELECT COUNT(Department_Id) FROM Employees;

SELECT COUNT(DISTINCT Department_Id) FROM Employees;

SELECT COUNT(*) FROM Employees;

It sorts the results in ascending order.

It excludes null values from the count.

It counts only the unique, non-null values in a column.

It counts all rows, including duplicates and nulls.

MONTHS_BETWEEN(date1 + date2)

MONTHS_BETWEEN(date1 - date2)

MONTHS_BETWEEN(date1, date2, format)

MONTHS_BETWEEN(date1, date2)

Join a table with another unrelated table

Join a table to itself

 Retrieve Distinct rows

Join multiple  tables in a database

FULL OUTER JOIN

INNER JOIN

LEFT OUTER JOIN

RIGHT OUTER JOIN

INNER JOIN

CROSS JOIN

OUTER JOIN

NATURAL JOIN

SELECT department_id, SUM(salary) AS Total_Salary

GROUP BY department_id;

SELECT department_id, TOTAL(salary) 

SELECT department_id, SUM AS  Total_Salary

SELECT department_id, SUM(salary) AS Total_Salary