Anyone know what this sign does?

Question

Good morning all,
Just a quick question. Ive tried googling this and checking my books but after an hour of doing so I just thought Id ask. Why would one use th (+) in a query, especially when joining two tables?
I saw this:
SELECT inv.item, inv.price, recpt.recept
FROM inventory inv, receipts recpt
WHERE inv.item(+) = recpt.item;
But dont know why you need that plus sign. Whats its purpose?

Answer 1

Spot the difference:
SQL> create table t1 as select level col from dual connect by level <= 3;
Table created.
SQL> create table t2 as select level col from dual connect by level <= 5;
Table created.
SQL> select col from t1;
       COL
         1
         2
         3
3 rows selected.
SQL> select col from t2;
       COL
         1
         2
         3
         4
         5
5 rows selected.
SQL> select t1.col t1col
  2  ,      t2.col t2col
  3  from   t1
  4  ,      t2
  5  where  t1.col = t2.col;
     T1COL      T2COL
         1          1
         2          2
         3          3
3 rows selected.
SQL> select t1.col t1col
  2  ,      t2.col t2col
  3  from   t1
  4  ,      t2
  5  where  t1.col(+) = t2.col;
     T1COL      T2COL
         1          1
         2          2
         3          3
                    5
                    4
5 rows selected.