How does indexing improve query performance?
Answers were Sorted based on User's Feedback
Answer / praveen
By creating index on single or multiple columns, query
takes index access path instead of full table scan. Full
table scan is costilier operation where it has to visit all
rows in the table whereas index operation just accesses the
index sub table with required hash value and joins with the
basetable using rowid. This improves response time and
performance of the query.
|Is This Answer Correct ?||28 Yes||3 No|
Answer / sri krishna
Teradata automatically Creates the Primary index , if not
specified by the DDl for Table .Some of the Other Types of
Partitioned Primary Index
Primary Index :- the PI is the way , Teradata Distributes
the Data , Accesses the Data to/from Amps. By Using the
Primary Index with Value or Range of Values in the Where
Clause of the Query , the operation Becomes a Single AMP/
Few amp aperation instead of all amp operation . the Access
Rowhash of the Pi is known --> Amp of the Column along
with rowid of the Column . (1 Amp Ops)
1. Highly Optimised Query Retrival
2. less Cost per Retrival
Secondary Index / Join Indexes :-
Creates a Secondary Index / Joinindex / Hashindex
Subtable , which maps the Column/s of the SI and the PI
Hash /Join(Frequently used Columns in two tables in this
Case ) , The operations , if using these Indexes are
basically 2 or more amp operation .
1. Quicker Query Retrival time than a full table scan .
2. costs less on the Resources than a FTS
3. the Performance is improved if the JI is used by the
1. Additional Space Req. for the Subtables
2. need to be droped and recreated for Loads to happen
(Multi Load , FastLoad)ect , which is a real PAIN !!!
3.still be a 2 amp operation when compared to PI Retrival
for a SI.
Partitioned Primary Indexes are Created so as to divide the
table onto partitions based on Range or Values as Required .
the data is first Hashed into Amps , then Stored in amps
based on the Partitions !!! which when Retrived for a
single partition / multiple Partitions , will be a all amps
Scan, but not a Full Table Scan !!!! . this is effective
for Larger Tables partitioned on the Date Specially !!!
there is no extra Overhead on the System (no Spl Tables
Created ect )
|Is This Answer Correct ?||19 Yes||5 No|
Answer / yuvaevergreen
PI is very important in TD, because the data distribution
is basically dependent on PI.
2.Fastest way to retrieve rows
3.Important for joins
|Is This Answer Correct ?||3 Yes||1 No|
Answer / guru
ONE LINE ANSWER: INdexing acts as SET option (Where clause)
while an query is being executed provided the query
contains these indexes.
Advanced Teradata Certified Professional
|Is This Answer Correct ?||1 Yes||5 No|
Does SDLC changes when you use Teradata instead of Oracle?
If the query is NOT WRITTEN PROPERLY then what are the recommendations you can give to the developer ?
I want to load 1000 rcds using. FL for every 100 records there is a check point.But script failed at 120 records, when we are restarting the script, it starts from last ckpt, but Target table contains populated data but FL doesnt support existing data in target table. How can we load data in FL?
what is identity columns in TD?
Find 2 highest sal from each dept who have completed 5 year in org
in ur table contains the coloumns like deptno,sal empname then i want output as deptno subtotalofdept totalsal 10 3700 3700 20 3400 7100 like that
I WANT TO LEARN TERA-DATA ,SO CAN ANY BODY PLZ REFER WHAT ARE THE TOPICS I HAVE TO GO THROUGH, TO GET ASAP JOB ,SO PLZ REFER ME WHERE I CAN GET NICE COACHING ON TERADATA.
IS IT POSSIBLE THAT THERE R TWO PRIMARY KEY WILL BE IN A SAME TABLE?PLZ HELP ME BY GIVING THE ANSWER.THANK U.
what is object level locking ? where do appear this type of locking ?
what is the structure of UV table in MLOAD?
can I use “drop” statement in the utility “fload”?
any one pls tell me what are the table names in banking project?