By understanding the keywords of the explain and how the optimizer works internally in terms of how SQL statements are executed on a Teradata system, you can assess the quality of each query. This information allows you to track down performance issues. Here are more keywords; if this doesn't match with your query nature and you suspect that this should not be in your explain, you might need to work on alternatives:
- JOINS: The following table explains the different types of joins and their uses:
|
Type of join |
Why this join? |
|
Nested join |
Least costly and fastest join. Happens on an equijoin with any index covering the join columns. |
|
Merge join |
Joining spool files are sorted normally by RowHash, with both have ... |
