how to select distinct value from multiple tables

Question

I need to get distinct values from 3 tables.

When I perform this code:

select DISTINCT(city) from a,b,c 

I get an error which says that

Answer 1

The UNION keyword will return unique records on the result list. When specifying ALL (UNION ALL) will keep duplicates on the result set, which the OP don't want.

SELECT city FROM tableA
UNION
SELECT city FROM tableB
UNION
SELECT city FROM tableC

• SQLFiddle Demo

RESULT

╔════════╗
║  CITY  ║
╠════════╣
║ Krakow ║
║ Paris  ║
║ Rome   ║
║ London ║
║ Oslo   ║
╚════════╝

Answer 2

SELECT city FROM A
UNION DISTINCT
SELECT city FROM B
UNION DISTINCT
SELECT city FROM C