MySQL: Select multiple values from a table based on multiple values from another table

I would like to return all the reports that are about each of these regions, that belong to a macroregion...

I would like to somehow

SELECT DISTINCT report FROM reports WHERE region = 
(SELECT distinct region from macroregions where macroregion = 开发者_JAVA百科'Africa') 

The regions in the macroregion are Sahara, West Africa, Tropical Africa,... etc

Although this is impossible since it the subquery would return multiple results.

SELECT DISTINCT report FROM reports WHERE 
region IN 
(SELECT distinct region from macroregions where macroregion = 'Africa') 

Maybe you missed IN operator

This should get you what you need:

SELECT 
    r.report
FROM
    reports r
INNER JOIN
    macroregions m ON 
        m.region = r.region
        AND 
        m.macroregion = 'Africa'

This is all of the reports associated to regions associated to the macroregion 'Africa'.