替代动态SQL和每个循环

Question

I need to execute the same select statement against 5 different instances of the same source db - 1 per clinic - and union the result set together for further processing. The existing script I've been tasked with maintaining executes a for each loop (1 iteration per instance) and substitutes the db name in the select statements for each iteration. Currently the db names are obtained from selecting the dbs from master where name in 'db 1, db2, db3, db4, db5'.

I'd prefer to hold a reference table with each of the db names and a flag for whether they are included. But is there an alternative to the for each loop?

Answer 1

So you have 5 different clinics and each one has a database with names: db1, db2, db3, db4, db5.

And the database names are all stored in a string variable as "db1, db2, db3, db4, db5" which you can then use as an array to sort through the database names.

Of course it seems clunky having all these different databases to have to deal with but looks like that is how things were when you got it and may have some advantages in that at least someone hacking or otherwise mishandling one clinic can't mess things up in the other databases.

And at least the looping isn't using something simple iteration like this:

For i = 1 to 5
    strDBName = "db" & i
Next

A problem with using i to iterate is that what if clinic 2 is no longer active and thus db2 should no longer be used. And of course it there is a new clinic added then the "For i = 1 to 5" would need to be changed all over to be "For i = 1 to 6".

So considering the above worse ways of doing things I kind of like the current way (DB names in a string variable that can be looped through as an array). And the idea of possibly "hold a reference table with each of the db names and a flag for whether they are included" to me seems like a fancy way of doing what you're already doing and personally I'm all in favor of "keep it simple" and "if it ain't broke don't fix it."

EDIT:
But the more I think about it taking your "hold a reference table with each of the db names and a flag for whether they are included" idea and running with it a little bit the following does seem natural (but of course perhaps be sure only Admin users can see any fields about the specific database):

Clinics Table with Fields Such As:
ClinicID
ClinicName
ClinicAddress
ClinicDBName - Note could store the DB name here
ClinicIsInactive