How can cross-database queries be implemented in Db2?

In Db2, cross-database queries can be achieved through three methods: cross-database references, join operators, and join expressions.

1. The table within the schema of the database.

SELECT t1.column1, t2.column2
FROM database1.schema1.table1 t1
JOIN database2.schema2.table2 t2
ON t1.column1 = t2.column1;

1. You can use join operators (such as JOIN, LEFT JOIN, INNER JOIN, etc.) to connect tables from different databases for querying. For example:

SELECT t1.column1, t2.column2
FROM database1.table1 t1
JOIN database2.table2 t2
ON t1.column1 = t2.column1;

1. Join expression: You can use join expressions to connect tables from different databases together for querying. For example:

SELECT t1.column1, t2.column2
FROM database1.table1 t1, database2.table2 t2
WHERE t1.column1 = t2.column1;

The above are the common methods for implementing cross-database queries in Db2, with the specific choice depending on the user’s needs and query scenarios.