Database Reference
In-Depth Information
Figure 10.2
ANSI Join Syntax.
More than two tables in a join forces specification of columns using
the USING or ON clauses, or both.
For the ANSI format, tables are joined from left to right. Thus join
conditions can only reference columns in the current join or from pre-
vious joins to the left. For the Oracle format, tables are joined from left
to right and top to bottom, allowing reference to any join condition in
the WHERE clause from anywhere in the WHERE clause.
Note:
When tuning using the Optimizer and the EXPLAIN PLAN com-
mand, in the deeper layers of Oracle tuning tools, these facts are not
always strictly true. For the purposes of this Oracle SQL topic, these facts
1
will suffice.
Now let's look at different types of joins you are able to build in Oracle.
10.2
Types of Joins
Let's look at the available types of joins and what exactly they do:
Cross-join or Cartesian product.
Merges all data selected from both
tables into a single result set.
