Teradata Interview Preparation Guide

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Teradata will redirect the new inserted row as per its PI to the target AMP (on the basis of its row hash value), and if it find same row hash value in that

AMP (hash synonyms) then it start comparing the whole row, and find out if duplicate.
If its a duplicate it silently skips it without throwing any error.

Global Temporary tables (GTT) -
1. When they are created, its definition goes into Data Dictionary.
2. When materialized data goes in temp space.
3. thats why, data is active upto the session ends, and definition will remain there upto its not dropped using Drop table statement.
If dropped from some other session then its should be Drop table all;
4. you can collect stats on GTT.

Volatile Temporary tables (VTT) -
1. Table Definition is stored in System cache
2. Data is stored in spool space.
3. thats why, data and table definition both are active only upto session ends.
4. No collect stats for VTT.

Performance tuning and optimization of a query involves collecting statistics on join columns, avoiding cross product join, selection of appropriate primary

index (to avoid skewness in storage) and using secondary index.

Avoiding NUSI is advisable.

The EXPLAIN facility is a teradata extension that provides you with an "ENGLISH" translation of the steps choosen by the optimizer to execute an SQL

statement.It may be used oin any valid teradata database with a preface called "EXPLAIN".

The following is an example:-

EXPLAIN select last_name,first_name FROM employees;

The EXPLAIN parses the SQL statement but does not execute it.

This provides the designer with an "execution stratergy".

The execution stratergy provides what an optimizer does but not why it choses them.

The EXPLAIN facility is used to analyze all joins and complex queries.

V2R6 included the feature of replica in it.in which copy of data base are available on another system.meam V2R6 provide the additional data protaction as

comprison to V2R5 while if data from one system has been vanishes.


After creating tables dynamically in the Teardata, where is the GRANT table option usually done ? When tables are newly created, what is the default role and

The GRANT option for any particular table depends on the privilages of the user. If it is an admin user you can grant privilages at any point of time.

The deafult roles associated with the newly created tables depend on he schema in which they are created.

A clique is a set of Teradata nodes that share a common set of disk arrays. Cabling a subset of nodes to the same disk arrays creates a clique.

Each AMP vproc must have access to an array controller, which in turn accesses the physical disks. AMP vprocs are associated with one or more ranks
(or mirrored pairs) of data. The total disk space associated with an AMP is called a vdisk. A vdisk may have up to three ranks. Hence Vdisk will communicate

with physical storage through array controllers.

BTEQ(Basic teradata query)

It allows us to write SQL statements along with BTEQ commands. We can use BTEQ for importing,exporting and reporting purposes.

The commands start with a (.) dot and can be terminated by using (;), it is not mandatory to use (;). SQL statements doesnt start with a dot , but (;) is

compulsary to terminate the SQL statement.

BTEQ will assume any thing written with out a dot as a sql statement and requires a (;) to terminate it.

There are 12 codd's rules applied to the teradata database

If you want to load, empty table then you use the fastload, so it will very usefull than the mutiload..because fastload performs the loading of the data in

2phase..and it noneed a work table for loading the data.., so it is faster as well as it follows the below steps to load the data in the table

Phase1-It moves all the records to all the AMP first without any hashing
Phase2-After giving endloading command, Amp will hashes the record and send it to the appropriate AMPS .

Multiload:

It does the loading in the 5 phases
Phase1:It will get the import file and checks the script
Phase2:It reads the record from the base table and store in the work table
Phase3:In this Application phase it locks the table header
Phase4:In the DML opreation will done in the tables
Phase 5: In this table locks will be released and work tables will be dropped.