Question

Have have two tables in two different databases:

Lets say i have Database users, and Database questions. If users has a table called USER_STATS that has

USER_ID,
EDU_INT1,
EDU_INT2,
EDU_INT3

, and questions has a table called questions that have a column called CLASS_SUBJECTS.

I want to run a query that will display * from QUESTIONS where CLASS_SUBJECTS equals either EDU_INT1,EDU_INT2,EDU_INT3 where the EDU_INT‘s are determined from a specific USER_ID

Any ideas? This is semi hard because of the two different databases

Answer 1

When querying across two databases, you just need to prepend the database name with a . before the table name as in database.table.column, and the database connection user must have access to both databases.

Beyond that, this a regular JOIN, but with a more complex ON clause using 3 conditions OR‘d together:

SELECT
  q.*
FROM 
  questions.questions q
  JOIN users.USER_STATS u ON (
    q.CLASS_SUBJECTS = u.EDU_INT1
    OR q.CLASS_SUBJECTS = u.EDU_INT2
    OR q.CLASS_SUBJECTS = u.EDU_INT3
  )
WHERE u.USER_ID = <some user id>