with recursive: provide ability to define recursive part as DERIVED table
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                 Key: CORE-4609
                 URL: http://tracker.firebirdsql.org/browse/CORE-4609
             Project: Firebird Core
          Issue Type: Improvement
            Reporter: Pavel Zotov
            Priority: Minor


It seems to me that definition of recursive part (e.g. expression below UNION 
ALL) as derived table does not conflicts with SQL standard.
For example, one might be done in postgress:
# with recursive c as (select 1 as i union all select x.i from (select c.i+1 as 
i from c where i<5) x ) select * from c;
 i
---
 1
 2
 3
 4
 5

The same ability we have in MS SQL.

Could you please add this feature in subsequent releases of FB ?

PS. 

I just read document "5WD-02-Foundation-2003-09.pdf", page 378 (on "paper" this 
is page 354). 
Could not understand all from this sentence:
------ beg of quote ------
WQEi shall not contain a <table subquery>TSQ that contains a <query name> 
referencing
WQNj, unless TSQ is a <derived table> that is immediately contained in a <table 
primary>
that is immediately contained in a <table reference> that is immediately 
contained in a <from
clause> that is immediately contained in a <table expression> that is 
immediately contained
in a <query specification> that constitutes a <simple table> that constitutes a 
<query primary>
that constitutes a <query term> that is immediately contained in a <query 
expression body>
that is WQEi
------ end of quote ------
-- but this: "unless TSQ is a <derived table>" - seems as hint that we *CAN* 
use DT in recursive part... :-)


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