SQL state: 42601 syntax error at or near "11" - postgresql

Question

I have a table address_all and it is inherited by several address tables. address_history inherits from parent table history_all and keeps current address information. I am creating new table which inherits address_all table and copies information from address_history to new table.
My stored procedure is like this below. I am having some error when I call it. To better explain error I am using line number.
1 CREATE OR REPLACE FUNCTION somefunc()
2 RETURNS void AS
3 $BODY$
4 DECLARE
5 year_id INTEGER;
6 month_id INTEGER;
7 week_id INTEGER;
8 addresstablename text;
9 backupdays text;
10 BEGIN
11 week_id := EXTRACT(DAY FROM TIMESTAMP 'now()');
12 month_id := EXTRACT(MONTH FROM TIMESTAMP 'now()');
13 year_id := EXTRACT(YEAR FROM TIMESTAMP 'now()');
14 addresstablename := 'address_history_' || week_id || '_' || month_id || '_' || year_id;
15 backupdays:= date_trunc('hour',CURRENT_TIMESTAMP - interval '7 days');
16 EXECUTE 'create table ' || addresstablename || '() INHERITS (address_all)';
17 EXECUTE 'insert into ' || addresstablename || ' select * from address_history where address_timestamp >= ' || backupdays || ''; --AS timestamp without time zone);
18 END;
19 $BODY$
20 LANGUAGE 'plpgsql' VOLATILE;
When I run:
select somefunc()
I get this error:
ERROR: syntax error at or near "12"
LINE 1: ...story where address_timestamp >= 2012-07-31 12:00:00-0...
^
QUERY: insert into address_history_7_8_2012 select * from address_history where address_timestamp >= 2012-07-31 12:00:00-04
CONTEXT: PL/pgSQL function "somefunc" line 14 at EXECUTE statement
********** Error **********
ERROR: syntax error at or near "12"
SQL state: 42601
Context: PL/pgSQL function "somefunc" line 14 at EXECUTE statement

Answer 1

Try this largely simplified form:
CREATE OR REPLACE FUNCTION somefunc()
RETURNS void AS
$func$
DECLARE
addresstablename text := 'address_history_' || to_char(now(), 'FMDD_MM_YYYY');
BEGIN
EXECUTE
'CREATE TABLE ' || addresstablename || '() INHERITS (address_all)';
EXECUTE
'INSERT INTO ' || addresstablename || '
SELECT *
FROM address_history
WHERE address_timestamp >= $1'
USING date_trunc('hour', now() - interval '7 days');
END
$func$ LANGUAGE plpgsql;
Major points:
You can assign variables in plpgsql at declaration time. Simplifies code.
Use to_char() to format your date. Much simpler.
now() and CURRENT_TIMESTAMP do the same.
Don't quote 'now()', use now() (without quotes) if you want the current timestamp.
Use the USING clause with EXECUTE, so you don't have to convert the timestamp to text and back - possibly running into quoting issues like you did. Faster, simpler, safer.
In LANGUAGE plpgsql, plpgsql is a keyword and should not be quoted.
You may want to check if the table already exists with CREATE TABLE IF NOT EXISTS, available since PostgreSQL 9.1.

Answer 2

Apparently you need to quote backupdays, or it is not seen as a string from where to parse a timestamp.

Answer 3

You're building SQL using string manipulation so you have to properly quote everything just like in any other language. There are a few functions that you'll want to know about:
quote_ident: quote an identifier such as a table name.
quote_literal: quote a string to use as a string literal.
quote_nullable: as quote_literal but properly handles NULLs as well.
Something like this will server you better:
EXECUTE 'create table ' || quote_ident(addresstablename) || ...
EXECUTE 'insert into ' || quote_ident(addresstablename) || ... || quote_literal(backupdays) ...
The quote_ident calls aren't necessary in your case but they're a good habit.