how-to-retrieve-data-from-multiple-objects-in-salesforce-with-one-query

Hey Joe,

If want to query records on multiple object in a single query then you have to use SOSL rather then SOQL query.

eg :

FIND {"Joe Smith" OR "Joe Smythe"}
IN Name Fields
RETURNING lead(name, phone), contact(name, phone)

but you can not perform DML operation.