MySQL - 如何将来自两个数据库的表组合成一个带有$ _GET的php查询字符串?

I want to query multiple tables data from two databases and display the data in a unique id php query string. e.g ?player=123456789. Both databases have a table that is storing a unique ID that will be used to show a players data. The ID tables between the databases cannot match eachother in any way. I want to mention that I know how to do this with one database at the time.

For example I have steamID for $db1 players and a playerID for $db2 players. There is no unique similarity between the IDs from each database. I am using intval($_GET['player']) to display data in the php query string. $db1 works fine if queried alone, so does $db2 but how can I combine the both to show in my query string? My code down below.

$db1 = 'SELECT * FROM `wm_round_stats` WHERE `steam_id_64`= '.intval($_GET['player']);
$db2 = "SELECT map, COUNT(killerId) AS totalkills
FROM hlstats_Events_Frags 
WHERE killerId='" intval($_GET['player']) "' GROUP BY map ORDER BY map";

WHERE killerId='" intval($_GET['player']) "' WHERE steam_id_64='" intval($_GET['player'])

How to combine these two above and both databases?

steamID is steam_id_64 and playerID is killerId in my code from my example above.

I am grateful for the help!