0 - 4 of 4 tags for left join

Hello,
This is a left join query and it consumes more than 40 minutes.
select
  table2.task_sk,
  table1.sub_sk,
  table1.sub_id,
  sum(table2.items) as items,
  sum(table2.amount) as amount,
  ...
from table1 left join table2
  on table1.sub_sk = table2.sub_sk and

 

Hi am new to Teradata and am stuck with a problem

 

There is an ID table which stores an Unique ID given to each person

 

I have read somewhere that Not exist will almost always perform better than Left join with null check in where clause,Can someone tell me the reason for this ?

eg :

SEL A.*

FROM TABLE A

WHERE NOT EXISTS

(SEL 1

FROM TABLE B

WHERE A.KEY=B.KEY

)

Would perform better than

 

There are three SQL statements (a, b & c) below, each of which performs a left join. Can anyone please explain how the execution of these statements differs from the other?

a) select c.c_name, a.n_name
from retail.client c left join retail.area a
on c.c_nationkey = a.n_nationkey
and a.n_name is null;