Question

I have a need for a single select statement that runs another select statement within its from clause and the result (there’s only one record) is the table name of the outer select.

For this purpose, I cannot use a stored procedure, exec, or @ variables.

Also, the query file must start with ‘select’ and contain only that statement.

I know there are better ways to accomplish the end result, however the vendor’s wizard that the query must run through sniffs for anything other than a single select statement. Its frustrating, but that’s all we have to work with.

Here is an example of what I am trying to do:

select
  plan.TransactionID,
  plan.PlanName,
  sum(plan.Value) as Rate 
from
  (select 'dbo._Result' + ltrim(str(CalculationID)) from dbo.Calculation where Name = 
    'TPRL Transaction Plan Rates'
  ) Plan

Of course, this does not work. However, neither does this:

select
  plan.TransactionID,
  plan.PlanName,
  sum(plan.Value) as Rate 
from
  exec(select 'dbo._Result' + ltrim(str(CalculationID)) from dbo.Calculation where Name = 'TPRL Transaction Plan Rates') Plan

Even though, this by itself does pull back the table I want into a result set:

exec(select 'dbo._Table' + ltrim(str(CalculationID)) from dbo.Calculation where Name = 'TPRL Transaction Plan Rates')

All I would need for it to do is treat the result as a literal (as in, macro substitution) in the from above, but it doesn’t work that way.

Is there a way in tsql to do this?

Answer 1

No, this cannot be done in just non-dynamic TSQL. In TSQL, table names can not be a variable or parametized, that can only be done with dynamic TSQL.

And dynamic TSQL can only be done with either EXEC('sql command') or sp_ExecuteSql(..).

Possible ways around this:
Unless the facility that you are using has its own macro substitution, then either

1. Have your client execute the inner SQL query first to determine the table name, then create a new file/string based on that. or
2. Use some kind of hacker SQL Injection tricks to fool your facility into thinking that you’re executing a SELECT when you are realling execuitng one of the dynamic SQL commands above.