Postgres return array from stored function - postgresql-9.4

Question

I am trying to return array from stored function and use it's output in a where clause , for a query. But it is not working for unknown reason. I really do not have clue. Please help.
Using below function.
CREATE OR REPLACE FUNCTION terep_cstm.testdays(
v_in_date date,
v_n integer)
RETURNS text[] AS
$BODY$
declare
listndays text = '';
arrndays text[];
BEGIN
for i in 0..v_n
loop
listndays = listndays||''||(v_in_date - i*interval '1 day')::date::text||',';
end loop;
listndays = trim(trailing ',' from listndays);
arrndays = string_to_array(listndays,',');
return arrndays;
END
$BODY$
LANGUAGE plpgsql VOLATILE;
Executing this query , with stored function.
select retl_code,price_2, attr_1,start_date,price,printedprice
from tessttable abc
where abc.attr_1 = '011' and abc.price_2 = '034' and abc.retl_code = '00068247'
and abc.start_date = ANY (select testdays('2017-05-31'::date,7)) --'2017-05-31'
--and abc.start_date = ANY (ARRAY['2017-05-31','2017-05-30','2017-05-29','2017-05-28','2017-05-27','2017-05-26','2017-05-25','2017-05-24'])
--and abc.start_date in ('2017-05-31','2017-05-30','2017-05-29','2017-05-28','2017-05-27','2017-05-26','2017-05-25','2017-05-24');
This is not working for ANY operator , with error message,
ERROR: operator does not exist: text = text[];
Please let me know where i am making mistake. The abc. start_date datatype is text and it is platform configured. Unfortunately we have no liberty to convert this column datatype and have to carry this one only.
It seems to work with
and abc.start_date = ANY (testdays('2017-05-31'::date,7));
But query gets hanged for a long time.As i could see the different in explain plan as well.
Query:
select retl_code,price_2, attr_1,start_date,price,printedprice
from tessttable abc
where abc.attr_1 = '011' and abc.price_2 = '034' and abc.retl_code = '00068247'
and abc.start_date in ('2017-05-31','2017-05-30','2017-05-29','2017-05-28','2017-05-27','2017-05-26','2017-05-25','2017-05-24');
Explain Plan:
"Index Scan using tessttable_comp_date on tessttable abc (cost=0.70..41.70 rows=1 width=43)"
" Index Cond: ((start_date = ANY ('{2017-05-31,2017-05-30,2017-05-29,2017-05-28,2017-05-27,2017-05-26,2017-05-25,2017-05-24}'::text[])) AND (prd_price_attr_1 = '011'::text) AND (price_2 = '034'::text) AND (retl_code = '00068247': (...)"
Query:
select retl_code,price_2, attr_1,start_date,price,printedprice
from tessttable abc
where abc.attr_1 = '011' and abc.price_2 = '034' and abc.retl_code = '00068247'
and abc.start_date = ANY (testdays('2017-05-31'::date,7)) ;
Explain Plan:
"Index Scan using tessttable_comp_date on tessttable abc (cost=0.70..10285844.48 rows=4 width=43)"
" Index Cond: ((prd_price_attr_1 = '011'::text) AND (price_2 = '034'::text) AND (retl_code = '00068247'::text))"
" Filter: (start_date = ANY (just_n_days('2017-05-31'::date, 7)))"

Answer 1

Get rid of the select, simply use the function as an expression:
and abc.start_date = ANY ( testdays('2017-05-31'::date,7) )
If abc.start_date is defined as date then you shouldn't compare a date value with an array of strings. Make the function return a date[] instead.
The function can also be simplified to a simple SQL function, there is no need for PL/pgSQL:
CREATE OR REPLACE FUNCTION testdays(v_in_date date, v_n integer)
RETURNS date[] AS
$BODY$
select array_agg(x::date)
from generate_series(current_date, current_date + 6, interval '1' day) x;
$BODY$
LANGUAGE sql;
To stick with the wrong text values for dates, just change what you aggregate
CREATE OR REPLACE FUNCTION testdays(v_in_date date, v_n integer)
RETURNS text[] AS
$BODY$
select array_agg(to_char(x, 'yyyy-mm-dd'))
from generate_series(current_date, current_date + 6, interval '1' day) x;
$BODY$
LANGUAGE sql;
Note that I changed the return type to date[] so that you will compare dates with dates.
However, I don't see why you need a function in the first place:
and abc.start_date between date '2017-05-31' and date '2017-05-31' + 7
would achieve exactly the same thing and will be faster in most of the cases.