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Use joins.

PHP код:

SELECT *
FROM usertable JOIN vehicletable
    ON usertable.vID = vehicletable.vID 


This will return all players that have a vehicle. If you want all players, even those who don't have a vehicle use LEFT JOIN.

PHP код:

SELECT *
FROM usertable LEFT JOIN vehicletable
    ON usertable.vID = vehicletable.vID 


Documentation: http://www.w3schools.com/sql/sql_join.asp