Comparing two dates with an insert trigger - sql

Question

I want to make sure that the suborder date is not before the orderdate using this trigger:::
CREATE OR REPLACE TRIGGER suborder_date before
INSERT ON suborder FOR EACH row DECLARE suborder_dd DATE;
orderdate DATE;
BEGIN
SELECT reqshipdate INTO suborder_dd FROM suborder;
SELECT orders.orddate INTO orderdate FROM orders;
IF orderdate < suborder_dd THEN
raise_application_error(-20002,('Required Ship Date is before Order Date'));
END IF;
END;
This compiles now I want to test it and insert this into the table...
insert into suborder values (1,1,'12-Jan-13','13-Jan-14', 'Office Depot', 1)
Error: Error starting at line 1 in command: insert into suborder
values (1,1,'12-Jan-13','13-Jan-14', 'Office Depot', 1) Error report:
SQL Error: ORA-01422: exact fetch returns more than requested number
of rows ORA-06512: at "BB.SUBORDER_DATE", line 4 ORA-04088: error
during execution of trigger 'BB.SUBORDER_DATE'
01422. 00000 - "exact fetch returns more than requested number of rows"
*Cause: The number specified in exact fetch is less than the rows returned.
*Action: Rewrite the query or change number of rows requested
With the help of others I finally got the output that I wanted when I edited the command for myself. Thank you!
CREATE OR REPLACE TRIGGER suborder_date BEFORE
INSERT ON suborder FOR EACH row DECLARE reqship DATE; orderdate date;
BEGIN
SELECT o.orddate
INTO orderdate
FROM orders o
WHERE o.orderno = :new.orderno;
IF orderdate > :new.reqshipdate THEN
raise_application_error(-20002, ('Required Ship Date is before Order Date'));
END IF;
END;

Answer 1

If you follow the comments, you should get something like this:
CREATE OR REPLACE TRIGGER suborder_date
BEFORE INSERT ON suborder
FOR EACH row
DECLARE
orderdate DATE;
BEGIN
SELECT o.orddate
INTO orderdate
FROM orders o
WHERE o.order_id = :new.order_id;
IF orderdate < :new.suborder_dd THEN
raise_application_error(-20002, ('Required Ship Date is before Order Date'));
END IF;
END;