Syntax error at or near "," - postgresql

Question

I have problems with this function and couldn't figure out how to fix it.
Create Function Quy(sdate timestamp)
returns integer as $$
declare
numbmonth integer;
quy integer;
Begin
numbmonth := Date_part('month',sdate);
If numbmonth < 4 then
quy := 1;
else if numbmonth < 7 then
quy := 2;
else if numbmonth < 10 then
quy := 3;
else quy := 4;
return quy;
END;
$$
LANGUAGE plpgsql;
This happens when I try to run the code:
ERROR: syntax error at or near ";"
LINE 16: END;
I really don't understand what is wrong with this.

Answer 1

Multiple syntax errors. The function would work like this:
CREATE OR REPLACE FUNCTION quy(sdate timestamp)
RETURNS integer AS
$func$
DECLARE
numbmonth integer := date_part('month', sdate);
quy integer;
BEGIN
IF numbmonth < 4 THEN
quy := 1;
ELSIF numbmonth < 7 THEN
quy := 2;
ELSIF numbmonth < 10 THEN
quy := 3;
ELSE
quy := 4;
END IF;
RETURN quy;
END
$func$ LANGUAGE plpgsql;
Consult the manual for the basic syntax of IF.
But that's much ado about nothing. To get the quarter of the year use the field specifier QUARTER with date_part() or EXTRACT() in a simple expression:
EXTRACT(QUARTER FROM $timestamp)
EXTRACT is the standard SQL equivalent of date_part().
Either returns double precision, so cast to integer if you need that (::int).
If you still need a function:
CREATE OR REPLACE FUNCTION quy(sdate timestamp)
RETURNS int LANGUAGE sql IMMUTABLE AS
'SELECT EXTRACT(QUARTER FROM $1)::int';
$1 is the reference to the 1st function parameter. Equivalent to sdate in the example. $-notation works in any version of Postgres, while named parameter references in SQL functions were only introduced with Postgres 9.2. See:
PLPGSQL Function to Calculate Bearing
dbfiddle here