SQL DISTINCT SELECT values from multiple tables

SQL DISTINCT SELECT eliminates duplicate records from the results, return only distinct (different) values.
DISTINCT aggregates: COUNT, AVG, MAX, etc.

so, it operates on one column and does not support multiple columns Suppose that in a table a column may contain many duplicate values

therefore sometimes you only want to list the different (distinct) values.

As a result SQL DISTINCT SELECT General syntax

SELECT DISTINCT column-name
  FROM table-name

1 2	SELECT DISTINCT column-name FROM table-name

used with COUNT and other aggregates

SELECT COUNT (DISTINCT column-name)
  FROM table-name

1 2	SELECT COUNT (DISTINCT column-name) FROM table-name

Another Example
Problem: List all Employee countries in alphabetical order.

SELECT DISTINCT Country
  FROM Employee
ORDER BY COUNTRY

SELECT DISTINCT Country

FROM Employee

ORDER BY COUNTRY

Result: 10 rows

Country
Australia
Brazil
Canada
Kenya
….

Employee
Id
Position
City
Country

Problem: List the number of Employee countries

SELECT COUNT (DISTINCT Country)
  FROM Employee

1 2	SELECT COUNT (DISTINCT Country) FROM Employee

Finally Result:

Employee
10

Resource
SQL

SQL DISTINCT SELECT values from multiple tables

As a result SQL DISTINCT SELECT General syntax

Problem: List the number of Employee countries

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