I try to take problem of iteration over ROW or RECORD variable from a
different perspective. I would to design a solution where isn't
necessary a conversion from binary value to text (this is a
disadvantage of hstore based solution). This mean so we have to have a
special instance of loop's body for every field of record (for every
field with different type then other field). Can we do it? Yes, we can
- we can use a similar access like polymorphic parameters - just used
not on function level, but on block level. We can iterate of record's
fields and for any distinct type we can do new instance of block
(loop's body) with new instances of included plans. I am thinking
about following syntax:
FOR varname OVER [row | rec variable]
LOOP {{body}}
END LOOP
this syntax isn't final. The real type of control variable is
specified in runtime and can be changed between iterations. But it
isn't problem, because for any unique data type we will have a
separate instance of {{body}}. control variable with name 'varname' is
redeclared for every iteration of cycle. This variable should be
writeable - so we are able to change any field of record. We can
define a automatic variable FIELDNAME that holds a name of processed
field.
so: sum over some row or rec var can be done with code:
CREATE rectype AS (x int, y int, f float);
DECLARE revar rectype;
BEGIN FOR f OVER recvar LOOP sum := sum + f; END LOOP; ...
or FOR f OVER recvar LOOP IF fieldname LIKE 'value%' THEN sum := sum + f; END IF; END LOOP;
some other examples:
FOR f OVER recvar
LOOP RAISE NOTICE '% => %', fieldname, f;
END LOOP;
FOR f OVER recvar
LOOP IF fieldname LIKE 'value%' THEN f := 0; END IF;
END LOOP;
What are you thinking of this proposal?
Regards
Pavel Stehule
