SQL (+)= definition and function

Question

I would like to know what this statement in SQL actually does:

select * 
from table 
where A (+)= B

I ran it against:

select * 
from table 
where A = B

and saw the difference but do not know how to formulate an explanation as to what (+)='s functionality is. It seems to me that (+)= is telling it to make it satisfy the condition A = B where available and ignore/enter as "empty" if components are not available.

Also, this statement is ran within a create view statement.

Thanks in advance.

Answer 1

(+)= is a used to show OUTER JOINS. It is not used now and is deprectaed now(as it is not very much readable). (+) denotes the "optional" table in the JOIN. Also I think that + notation is only present for backwards compatibility because Oracle debuted it before the ANSI standard for joins was put in place.

Also note that Oracle recommends that you use the FROM clause OUTER JOIN syntax rather than the Oracle join operator.

Outer join queries that use the Oracle join operator (+) are subject to the following rules and restrictions, which do not apply to the FROM clause OUTER JOIN syntax:

• You cannot specify the (+) operator in a query block that also contains FROM clause join syntax.
• The (+) operator can appear only in the WHERE clause or, in the context of left-correlation (when specifying the TABLE clause) in the FROM clause, and can be applied only to a column of a table or view.
• If A and B are joined by multiple join conditions, then you must use the (+) operator in all of these conditions. If you do not, then Oracle Database will return only the rows resulting from a simple join, but without a warning or error to advise you that you do not have the results of an outer join.
• The (+) operator does not produce an outer join if you specify one table in the outer query and the other table in an inner query.
• You cannot use the (+) operator to outer-join a table to itself, although self joins are valid. For example, the following statement
  is not valid:

-- The following statement is not valid:
     SELECT employee_id, manager_id 
    FROM employees
    WHERE employees.manager_id(+) = employees.employee_id;

However, the following self join is valid:

   SELECT e1.employee_id, e1.manager_id, e2.employee_id
    FROM employees e1, employees e2
    WHERE e1.manager_id(+) = e2.employee_id
    ORDER BY e1.employee_id, e1.manager_id, e2.employee_id;

• The (+) operator can be applied only to a column, not to an arbitrary expression. However, an arbitrary expression can contain one or more columns marked with the (+) operator.

• A WHERE condition containing the (+) operator cannot be combined with another condition using the OR logical operator.

• A WHERE condition cannot use the IN comparison condition to compare a column marked with the (+) operator with an expression.

Answer 2

See oracle doc here: http://docs.oracle.com/cd/B19306_01/server.102/b14200/queries006.htm

(go down to outer joins)

An outer join extends the result of a simple join. An outer join returns all rows that satisfy the join condition and also returns some or all of those rows from one table for which no rows from the other satisfy the join condition.