MySQL - vyberte 3 tabulky se správnou levou syntaxí spojení

zkuste to (bez použití poddotazu )

SELECT  a.name, b.cars, count(c.id) as  number
FROM    users a 
            INNER JOIN data_tmp b
                on a.who = b.who
            LEFT JOIN data c
                on a.who = c.who AND
                   a.name = c.name
WHERE    a.who = 2 
GROUP BY a.name, b.cars

toto funguje na různých serverech:

MSSQL SERVER @ SQLFIDDLE
MYSQL @ SQLFIDDLE