Question

I have 2 databases namely db1,db2. I need a query that fetch the data from these dbs(db1,db2) which have inturn 2 tables(concessions,invoicing) each.

In db1.concessions => concession is primary key.
db1.invoicing => [Concession Number] is primary key

similarly in db2.concessions => concession is primary key.
db2.invoicing => [Concession Number] is primary key

In database1

db1.tbl1 => Concessions table has data

    concession
    TH-123
    TH-456
    FP-789
    NZ-609

db1.tbl2 => invoicing table has data

    [Concession Number]          invoiced_on
    TH-322                        10.09.10
    TH-900                        23.10.10
    FP-675                        04.05.09
    NZ-111                        19.11.08

luckily, in a database the value of concession in unique. i.e concessions.[concession] = invoicing.[concession Number] yields no data..

In database2:

db1.tbl1 => Concessions table has data

    concession
    TH-123
    FP-789
    NZ-999
    TH-900

db1.tbl2 => invoicing table has data

    [Concession Number]          invoiced_on(dd.mm.yy)
    TH-456                        18.01.06
    TH-777                        23.10.04
    FP-675                        03.05.09
    NZ-149                        26.11.08

HEre in db2 concession is unique, concessions.[concession] = invoicing.[concession Number] yields no data..

Now the query should fetch the records that have common
db1.(concessions.concession OR invoicing.concession number) = db2(concessions.concession OR invoicing.concession number)

In the sample data it should return, TH-123,FP-789,NZ-999, FP-675.

My 2nd question is there is possibility of extending this query to multiple database. I can’t change the count of databases to 1 as they are already fixed. Please let me know the best procedure for the same.

I tried something like this, there are syntax errors,

SELECT a.concession as db1_CON_NUMBER FROM db1.dbo.concessions as a  UNION 
SELECT b.[Concession Number] as db1_CON_NUMBER  FROM db1.dbo.invoicing as b 
INNER JOIN 
SELECT c.concession as db2_CON_NUMBER FROM db2.dbo.concessions as c  UNION 
SELECT d.[Concession Number] as db2_CON_NUMBER  FROM db2.dbo.invoicing as d 
ON db1_CON_NUMBER = db2_CON_NUMBER 

Hope you will answer both the questions.
Thanks for your patience in reading such a long mail!

Answer 1

You can reference other databases directly if the user has permissions.

<database>.<user>.<tablename>

Is the full “path” to the database table.

Often you use

db1.dbo.tbl1 join db2.dbo.tbl2

where dbo is default for database owner, any table not owned by a specific user is owned by dbo by default.

UPDATE

To get the query to validate you can expand it to this

SELECT * FROM 
(SELECT a.concession as db1_CON_NUMBER FROM db1.dbo.concessions as a  
UNION 
SELECT b.[Concession Number] as db1_CON_NUMBER FROM db1.dbo.invoicing as b ) c

INNER JOIN 

(SELECT c.concession as db2_CON_NUMBER FROM db2.dbo.concessions as a 
UNION 
SELECT b.[Concession Number] as db2_CON_NUMBER FROM db2.dbo.invoicing as b ) d

ON db1_CON_NUMBER = db2_CON_NUMBER 

But I have not had time to check if this would return the right data but you can test.