Firebird 2.1 Language Reference Update

DML statements
for with my_rivers as (select * from rivers where owner = 'me')
select name, length from my_rivers into :rname, :rlen
do
begin
..
end
Recursive CTEs
A recursive (self-referencing) CTE is a UNION which must have at least one non-recursive member, called the
anchor. The non-recursive member(s) must be placed before the recursive member(s). Recursive members are
linked to each other and to their non-recursive neighbour by UNION ALL operators. The unions between nonrecursive
members may be of any type.
Recursive CTEs require the RECURSIVE keyword to be present right after WITH. Each recursive union member
may reference itself only once, and it must do so in a FROM clause.
A great benefit of recursive CTEs is that they use far less memory and CPU cycles than an equivalent recursive
stored procedure.
The execution pattern of a recursive CTE is as follows:
• The engine begins execution from a non-recursive member.
• For each row evaluated, it starts executing each recursive member one-by-one, using the current values from
the outer row as parameters.
• If the currently executing instance of a recursive member produces no rows, execution loops back one level
and gets the next row from the outer result set.
Example with a recursive CTE:
with recursive
dept_year_budget as (
select fiscal_year,
dept_no,
sum(projected_budget) as budget
from proj_dept_budget
group by fiscal_year, dept_no
),
dept_tree as (
select dept_no,
head_dept,
department,
cast('' as varchar(255)) as indent
from department
where head_dept is null
union all
select d.dept_no,
d.head_dept,
d.department,
h.indent || ' '
from department d
join dept_tree h on d.head_dept = h.dept_no
)
70