basic questions


basic questions

Hi Experts,

Request you to spare the time to shed some light on below.

1.   "You might pick a NUPI over an UPI because the NUPI column may be more effective for query access and joins"

so, if a column is a candidate for UPI, should it be selected as NUPI for the above mentioned effectiveness.  What kind of effectiveness is achieved by selecting a NUPI over a column that can act as a ideal UPI?

2.  Why database links are not used to connect from one database to another database in Teradata.

3. How is NOPI different from UPI/NUPI tables in performance wise as even NOPI is hashed on random column (I guess)

4. The rows will be fetched from AMPS are based on hash value (not on the column value), how does it handle HASH SYNONYM

say 'ename' column is NUPI and has values 'vikram','abc' that will results in same hash value and hence to same amp.  If I write a select query  as

select * from emp where ename='vikram'

does it return only the row 'vikram' or both 'vikram' and 'abc'  as the matching of records are done in AMP through rowhash. 

5.  If amp is full and again new record has hash value to other amp, then will it be inserted or does it throw an error.


Re: basic questions

Well, looks like all are busy.  Was expecing some answers on this.