Declaring timestamp in postgres - sql

Question

I have to insert a timestamp value into a table. I am inserting values by writing an stored procedure.
This is the code to my stored procedure.
CREATE OR REPLACE FUNCTION dataInsert_Schedule() RETURNS boolean As
$$
DECLARE
i integer;
j integer;
dur integer;
tup Channel%rowtype;
BEGIN
FOR tup IN SELECT * FROM Channel
LOOP
for i in 0..6 LOOP --days
for j in 0..23 LOOP --hours
dur = round((random() * 2) + 1);
IF i + dur > 24 then
dur = 24 - i;
END IF;
INSERT INTO Schedule VALUES(tup.Channel_ID, round((random() * 999) + 1),( current_date + (integer to_char(i,'9')) )+ (interval to_char(j,'99') || ' hour'), (interval dur ||' hour'));
i = i + dur - 1;
END LOOP;
END LOOP;
END LOOP;
return true;
END
$$ LANGUAGE plpgsql;
When I write the query Select * From dataInsert_Schedule(); I got the following error :
ERROR: syntax error at or near "to_char"
LINE 1: ...d((random() * 999) + 1),( current_date + (integer to_char( $...
^
QUERY: INSERT INTO Schedule VALUES( $1 , round((random() * 999) + 1),( current_date + (integer to_char( $2 ,'9')) )+ (interval to_char( $3 ,'99') || ' hour'), (interval $4 ||' hour'))
CONTEXT: SQL statement in PL/PgSQL function "datainsert_schedule" near line 15
********** Error **********
ERROR: syntax error at or near "to_char"
SQL state: 42601
Context: SQL statement in PL/PgSQL function "datainsert_schedule" near line 15
I First tried this
INSERT INTO Schedule VALUES(tup.Channel_ID, round((random() * 999) + 1),( current_date + (integer ''||i) )+ (interval (j ||' hour')), (interval dur ||' hour'));
way of inserting, but I was getting the same kind of error.
Why I am getting this error?
And the schedule table is defined as following:
CREATE TABLE Schedule(
Channel_ID Integer REFERENCES Channel(Channel_ID),
Program_ID Integer REFERENCES Program(Program_ID),
Start_Time Timestamp NOT NULL,
Duration Interval NOT NULL,
CONSTRAINT Schedule_Key PRIMARY KEY(Channel_ID, Program_ID)
);

Answer 1

It works for me like this:
select (to_char(1,'99') || ' hour')::interval;
You don't need the to_char:
select (1 || ' hour')::interval;
interval
----------
01:00:00
So this would be it:
INSERT INTO Schedule
VALUES (
tup.Channel_ID,
round((random() * 999) + 1),
(current_date + i::integer) + (j || ' hour')::interval,
(dur ||' hour')::interval
)

Answer 2

A type name may be specified before a string constant to cast it into this type, but it applies only to constants. So integer '123' is fine but integer to_char(something) or interval column_name are not permitted, which is why your query fails.
This is explained in the SQL syntax chapter from the manual, specifically this paragraph: Constants of Other Types.
Excerpt:
A constant of an arbitrary type can be entered using any one of the
following notations:
type 'string'
'string'::type
CAST ( 'string' AS type )
and below:
The ::, CAST(), and function-call syntaxes can also be used to specify
run-time type conversions of arbitrary expressions
The point relevant to the question being that type 'string' notation is not included in the syntaxes that can accept arbitrary expressions, contrary to :: and cast().