Join Plan With or Without Nested Join | Join Planning/Optimization | Vantage - 17.10 - Join Plan Without Nested Join - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - SQL Request and Transaction Processing

Product
Advanced SQL Engine
Teradata Database
Release Number
17.10
Release Date
July 2021
Content Type
Programming Reference
User Guide
Publication ID
B035-1142-171K
Language
English (United States)

About a Join Plan Without Nested Join

Without using a nested join, the Optimizer generates the following join plan:

Operation Joined Tables Total Processing Time
Spool 1:product join duped table_1,

direct table_2

1 hour 15 minutes

The total estimated completion time is 1 hour 15 minutes.

EXPLAIN Output for Unoptimized Join Plan

The following partial EXPLAIN output is generated when nested joins are not used:

2) Next, we do an all-AMPs RETRIEVE step from test.tab1 by way of an
   all-rows scan with no residual conditions into Spool 2, which is
   duplicated on all AMPs. The size of Spool 2 is estimated to be 4
   rows. The estimated time for this step is 0.08 seconds.
3) We do an all-AMPs JOIN step from Spool 2 (Last Use) by way of an
   all-rows scan, which is joined to test.tab2. Spool 2 and test.tab2
   are joined using a product join, with a join condition of
   (“Spool_2.y1 = test.tab2.y2"). The result goes into Spool 1, which 
   is built locally on the AMPs. The size of Spool 1 is estimated to
   be 2 rows. The estimated time for this step is 1 hour and 15 
   minutes.