针对每个DB运行查询

Question

Im using php to do this:

while ($row = mysql_fetch_object($db_list)) {
 echo $row->Database . "<br>";

}

DB1 DB2 DB3 DB4

I want to add to this by adding a simple select query and running that against each database. the select will pull out the firstname of every user in the users table from each DB.

Answer 1

Try following

(SELECT username, 'DB1' AS Database FROM DB1.users)
UNION ALL
(SELECT username, 'DB2' AS Database FROM DB2.users)
UNION ALL
...etc

Changed UNIONs to UNION ALL