MySQL: Select Distinct from 2 different tables?

Use distinct and union:

select distinct product_type from table1
union
select distinct product_type from table2

The union will remove duplicates when combining the results.

Use a distinct with a subquery which contains a union

select distinct product_type from (
    select product_type from table 1
    union 
    select product_type from table 2
) t

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