Wanted to understand what is the fucntion of - diagnostic noaggrenh on for session scritp.. What does this do?
Read a couple of blogs, it said if there a SQL with "select & Group By" clause, then the actual table count v/s the sel statement executed with group by clause, the counts would appear different. "select & Group By" would result in less no. of records when compared to normal "Select count(*)", in order to negate that, we use "diagnostic noaggrenh".
Is that the actual use? We are using this as the 1st statement to be executed before we run DELETE / INSERT macro. Hence asking what would this actually do?
In TD13, Teradata improved the performance of aggregations. One of the primary things in this group of aggregation enhancements was work to improve the performance of Distinct and Group by, and eliminate the difference in performance that people were seeing if they used one versus the other.
This diagnostic turns off these enhancements.
I would recommend you only use this diagnostic if you are requested to by the GSC.