How to nest anonymous blocks with declare statements in Firebird? - sql

Question

In Firebird, DECLARE statements can be listed at the beginning of an EXECUTE BLOCK statement:
EXECUTE BLOCK [(<inparams>)]
[RETURNS (<outparams>)]
AS
[<declarations>]
BEGIN
[<PSQL statements>]
END
Within a block, no further DECLARE statements are possible, i.e. all variables are globally scoped, for the entire block. Is there any workaround to declare local variables for the scope of a nested block only, in Firebird? Nesting EXECUTE BLOCK calls isn't possible:
EXECUTE BLOCK AS
DECLARE i INTEGER;
BEGIN
EXECUTE BLOCK AS -- This doesn't compile
DECLARE j INTEGER;
BEGIN
END
END

Answer 1

You can't nest execute block statements. The design of this feature did not consider this option. In Firebird 3, you can define 'sub-procedures' or 'sub-functions', but those don't have access to variables or input columns from the outer-level (so they only provide an isolated scope, and you'd need to explicitly pass in values using parameters, and out using returning values), and you can't nest more than one level.
For example:
execute block
returns (firstval integer, secondval integer)
as
declare function x(param1 integer) returns integer
as
declare var1 integer;
begin
var1 = param1 * 2;
return param1 + var1;
end
begin
firstval = 1;
while (firstval < 10) do
begin
secondval = x(firstval);
suspend;
firstval = firstval + 1;
end
end
https://dbfiddle.uk/?rdbms=firebird_3.0&fiddle=677b33e416bd3f6a6a34e060d9afce9e
I am not aware of other options to declare variables with a limited scope in Firebird PSQL.