MySQL LIMIT within JOIN
For a correlated subquery you should use a CROSS APPLY, unfortunately MySql doesn't allow it, but you can simulate it on this way:

SELECT     `symbols`.`id`, 
           `symbols`.`symbol`, 
           `statistics`.
           `marketCapitalization`,
           `s`.`companyId`,
           `s`.`marketCapitalization`  
FROM       `symbols` 
INNER JOIN `company_key_statistics` `s`
ON         `s`.`pk` = (SELECT `pk`          -- the PK of company_key_statistics
                       FROM   `company_key_statistics`
                       WHERE  `companyId` = `symbols`.`id` 
                       ORDER by `createdAt` 
                       DESC LIMIT 1) 
WHERE  `symbols`.`symbol` IN ('ORCL', 'SNAP');


You can find some example on SO.