How does PHP write statements for queries between multiple databases?

How does PHP write statements for queries between multiple databases? Two data tables, table1table2table1 & nbsp; table2 & nbsp in database1; in database2, how can I query data in table2 through table1? ------ Solution ------------------ in the table PHP, how do I write statements for queries between multiple databases?
Two data tables
Table1
Table 2
Table1 in database1
Table2 in database2
How can I query data in table 2 through table1 data?

------ Solution --------------------
Add the database name before the table name, with the condition that the current user has access to both databases.

Select * from database1.table1, database2.table2 where...
------ Solution --------------------
If the two databases can be accessed using the same account password, you can use
Database1.table1
Database2.table2
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