Database Reference
In-Depth Information
Right-Deep Trees
A
right-deep tree
, as shown in Figure
14-3
, is a join tree where every join has a table in its left input. This join tree is
rarely chosen by the query optimizer.
Figure 14-3.
In a right-deep tree, the left input is always a table
The following execution plan illustrates the join tree depicted in Figure
14-3
. Note that the first child (that is, the
left input) of each join operation (that is, lines 2, 4, and 6) is a table:
-------------------------------------
| Id | Operation | Name |
-------------------------------------
| 0 | SELECT STATEMENT | |
| 1 | HASH JOIN | |
| 2 | TABLE ACCESS FULL | T1 |
| 3 | HASH JOIN | |
| 4 | TABLE ACCESS FULL | T2 |
| 5 | HASH JOIN | |
| 6 | TABLE ACCESS FULL| T3 |
| 7 | TABLE ACCESS FULL| T4 |
-------------------------------------
