What does =+ mean in an Oracle query

Question

Normally in C++ programming language, the plus means addition, in the example below

int x;
x += 1;

However in plsql query, I am confused about the same usage. That usage does not mean addition. In that case, what is the meaning of =+ ?

Select c.* From alf_numeric a, run_of_id b, tail_of_st c 
WHERE category_id IN(33,36) AND a.flow_id =+ b.flow_id 

Any idea?

Answer 1

This:

...
FROM alf_numeric a, run_of_id b 
WHERE a.flow_id = b.flow_id (+)

would mean:

...
FROM alf_numeric a
  LEFT JOIN run_of_id b 
    ON a.flow_id = b.flow_id 

---

My guess is that:

a.flow_id =+b.flow_id 

is parsed as the (simple):

a.flow_id = (+b.flow_id)

and so is the same as:

a.flow_id = b.flow_id