Teradata Interview Questions And Answers For Freshers and Experienced. Here Mindmajix shares top real-time Teradata questions. These interview questions are prepared by the Teradata experts and asked during many Teradata interviews. We are sure that these Teradata SQL interview questions will help to crack your next interview. Learn Now!
Below mentioned are the Top Frequently asked Teradata Interview Questions and Answers that will help you to prepare for the Teradata interview. Let's have a look at them.
|Types of Teradata Interview Questions|
|If you want to Enrich your career with a Certified Teradata Specialist, then enroll in “Teradata Training” - This course will help you to achieve excellence in this domain.|
|Tera Data||Basic RDBMS|
|It has a large number of heterogeneous destinations||They lack the same|
|Source operation is allowed||It is not necessary always|
|Components can be used again and again without any limit||Component reusability is limited|
|It is easy to debug the Teradata||Debugging is difficult|
Teradata is basically a relational database management system that is known due to some of its vast and useful features that are best enough to be considered for a number of tasks that are related to the data. It is considered when it comes to driving the datamart, OLAP, and data warehouse applications of a business. It is best enough to b considered when it comes to managing the parallel processing of the data simply in no time.
|Explore Teradata Tutorial for more information|
Well, it is capable to be considered for performing multiple tasks. However, it is widely considered as best for taking and storing the requests in a queue. It can help in storing a very large number of requests in a defined manner. The multiple sets of responses can easily be created after this and the users can save time and effort both.
The two common ETL tools are Informatica and DataStage.
Yes, the same is possible and the users are free to do the same provided some basic conditions are fulfilled by them. This can be done by performing execution in UNIX.
Well, data is the real source of deriving useful information and without data, many important tasks such as business management, decision making, problem formulation, and many other tasks that are useful cannot be accomplished easily. When the same is not managed, there are strong chances that the user will get errors in all of the above tasks. A well-managed data always enable users to save time and to locate things easily. There are a lot of other reasons as well due to which data management is important.
It is basically an add-on feature in Teradata which simply lets the users share the cache simply with all the applications. This is because it works closely with the source and even lets the users mold the outcomes in the manner they are comfortable with. This approach lets them save time when the data is complex and has so many errors associated with them.
While managing the data and handling other tasks related to it, the users have to make sure that there is effective communication between the applications and the PE’s that are considered. For this, a software called Channel Driver is used. Generally, it acts as a direct link between them and enables clients to share information easily.
Gateways are quite similar to that of Channel driver but the only difference is they enable the communication of PE and applications in the case of network clients or for the clients who are attached to the network.
This can be done with the help of a feature called Tpump which is actually a dedicated one for controlling and monitoring the traffic.
This can be done with the help of two useful methods. The users can go ahead with running the old file without dropping the error table completely. Rather than rectifying the errors, they can execute the command again and again. The other method that can enable them to simply keep up the pace is running a new file. Basically, the script is executed in this process and something which helps them in this matter ends to load and beginning table. This generally removes all the barriers from the tables and the entire script can be run again easily.
Access Module Processor is actually loaded with the Database Manager subsystems. IT is because of no other reason the tasks that can easily be performed through it are performing DDL, DML, implementation of Joins and Aggregations, applying, and as well as releasing of the locks.
This can be done with the help of a sub-feature known as CSUM.
It is not always necessary that these components are applied at the same time. Depending on the task, a specific or all of them can be used for getting the outcomes.
In complex applications, there is no such limit on how one Gateway is assigned per node during general use.
It can be checked easily with the following command
In Teradata, all the AMP are allowed to operate separately and they cannot be clubbed with USI especially when multi operations are executed at the same time. NUSI is a better approach that can easily be clubbed and a lot of time can be saved.
Parallel Data Extension is actually an interface layer that is responsible for operating the data in a parallel mode. In most cases, the volume of the data really doesn’t matter and the users are free to generate outcomes that are simply the best. This layer is present above the Operation system layer.
While using Teradata, the users are free to take advantage of a supreme feature for this. All the Vprocs are set to automatically move to the parallel nodes from the one that gets fails and thus, the data can easily be recovered without making complex efforts.
It is actually a general compilation of a large group of cylinders that are nothing but disks. The users also call it the Disk Array. It is done to assure that in case of an emergency, the loss to the data is minimum as the same is already divided into the segments. It is possible to create backups and the users are therefore free to derive the outcomes accordingly.
Yes, the users can perform this task, and generally, for this, a process known as parsing is considered. The process simply checks the different types of errors such as syntactical and, semantics. In addition to this, it can also be considered for the purpose of checking whether the object exists actually or not.
Access Module Processor is a virtual processor that is responsible for managing and controlling a single segment of a database. It is not possible by any other Access Module Processor to share the same. Thus, it is also called a secure or shared-nothing architecture.
It is basically an approach that is responsible for enabling the users to handle all the SQL requests and then provide responses in the SQL. There are several software components present in it and the users are free to split the SQL into different sections. These sections are then transferred to the AMP in a defined or in random manner.
Data management simply means managing a volume of data that is generally measurable or when the data size is small. It doesn’t take a lot of effort even if the data is unstructured. The data is mostly a part of any large group in this approach. On the other side, database management is a bit different from data management although they both seem similar. In this, the volume of data is high and data can have multiple sources and types which are stored at a specific location. Managing the entire database is a bit difficult and sometimes needs time.
PPI stands for Partition Primary Index and is basically a feature used for storage purposes. The storage is in the middle range and avoids the need for a complete table scan.
Teradata has many useful components and the users are always free to get the desired outcomes in the shortest possible time. A few of them are widely used and play a significant role in making the tasks simple are spotlighted below.
There is a command known as “Update else Insert” (USERT) which is available only in Teradata.
The failure of the node is one of the major problems in Teradata. Although the chances are less, it creates several glitches when happens. There is a dedicated feature in Teradata to control this situation and i.e. creating a Clique. The same is actually an assortment of nodes that are shared between the drives which are common. When this approach is considered, the failure of one node doesn’t make much impact.
It is used for running the queries
In Teradata, Journals are placed on the system to provide data availability in the absence of process failure. There are two types of journals are available are Recovery Journals and Permanent Journals.
Teradata BTEQ Exports are four types, they are
Tables can be created using CREATE TABLE statement, CREATE TABLE a statement with column definition, CREATE TABLE from an existing table, CREATE TABLE statement with a SELECT statement.
We can find duplicate records using the DISTINCT or GROUP BY statement.
Finding Duplicate Records Using DISTINCT statement:
SELECT DISTINCT column 1, column 2… FROM tablename; Finding Duplicate Records Using GROUP BY statement: SELECT column 1, column 2,… FROM tablename GROUP BY column 1, column 2….;
By using SELECT HASHAMP() + 1; query we can find the number of AMPs.
SELECT HASHMAP (HASHBUCKET(HASHROW(primaryindexvalue))), COUNT(*)
FROM table-name GROUP BY 1;
The above query identifies the number of rows in each AMP for a particular database table.
It's one type of error in Teradata. Spool Space Error will trigger when intermediate results of the query exceed the AMP spool space limit set for a user.
TENACITY command in Teradata specifies the total waiting time to establish a new connection.
In Teradata, NUSI and FTS will access all the AMPs, but the difference is,
In Teradata FAST EXPORT refers to exports data from Teradata to a Flat file.
Teradata Multiload supports up to five populated tables.
The transient journal is a system-maintained dictionary table that provides a way to protect transactions from various system failures and from deadlock (see SQL Request and Transaction Processing for a description of deadlock). Each transaction processed by Teradata Database records a before change image of rows that are touched by the transaction.
Then if a transaction fails for some reason, the before change image of any modified rows can be retrieved from the transient journal and written over the modifications, returning the row to the same state it was in before the transaction occurred. Teradata Database removes all before change images from the transient journal after a transaction commits.
A database privilege is a permission to access or to manipulate a database object or data. Specific privileges are required for nearly everything that can be done in the Teradata Database.
Teradata Database privileges are used by administrators to control access to database objects and data and to control the types of actions and activities available to users.
The privileges are used to control which users can:
Teradata Database supports system-level, object-level, row-level, and zone-level privileges.
GIVE statement transfers ownership of a database or user space to another user. Also transfers all databases and users owned by the transferred database or user.
GIVE database_name TO recipient_name
GIVE user_name TO recipient_name
GRANT establishes explicit privileges for one or more users, proxy users, databases, or roles.
In Teradata there are different GRANT forms are there, they are:
The GRANT (SQL Form) controls access to, and manipulation of, database objects, while the GRANT (MONITOR form) privilege set relates to monitoring system-wide performance. To grant a user all privileges, including MONITOR, you must perform both of the following requests:
GRANT ALL PRIVILEGES ON object TO user WITH GRANT OPTION; GRANT MONITOR PRIVILEGES TO user WITH GRANT OPTION;
REVOKE rescinds explicit privileges from one or more users, proxy users, databases, or roles. The privileges might have been conferred either automatically or by a previous GRANT statement.
SHOW statements return the result of the last data definition statement performed against the named database object in the form of a CREATE database_object or ALTER database_objectstatement.
Hot Standby Node (HSN) is a node that is a member of a clique that is not configured (initially) to execute any Teradata process.
The primary index for a volatile table can be nonpartitioned or row-partitioned. The table can also be defined without a primary index (NoPI).
The following options are not permitted for volatile tables.
Global temporary and volatile tables permit you to define whether their activity is logged to the transient journal. While the NO LOG option reduces the system overhead of logging, it is also true that table modifications are lost and cannot be recovered upon an aborted SQL request.
The permanent journal is a user-specified table that can be used to capture both before images and after images of Teradata Database transactions. Journal entries in this table can be used by the Archive/Recovery utility to roll forward or rollback transactions during a recovery operation.
The MERGEBLOCKRATIO option provides a way to combine existing small data blocks into a single larger data block during full table modification operations for permanent tables and permanent journal tables. This option is not available for volatile and global temporary files. The file system uses the merge block ratio that you specify to reduce the number of data blocks within a table that would otherwise consist mainly of small data blocks.
Use this option to set the temperature-based block compression state of a table.
Teradata Virtual Storage tracks data temperatures at the level of cylinders, not tables, and the file system obtains its temperature information from Teradata Virtual Storage, so it also handles temperature-related compression at cylinder level.
Situations sometimes occur where the identification and choice of a simple primary key are difficult, if not impossible. There might be no single column that uniquely identifies the rows of a table or there might be performance considerations that argue against using a composite key. In these situations, surrogate keys are an ideal solution.
A surrogate key is an artificial simple key used to identify individual rows uniquely when there is no natural key or when the situation demands a simple key, but no natural non-composite key exists. Surrogate keys do not identify individual rows in a meaningful way: they are simply an arbitrary method to distinguish between them.
CHECK constraints are the most general type of SQL constraint specification. Depending on its position in the CREATE TABLE or ALTER TABLE SQL text, a CHECK constraint can apply either to an individual column or to an entire table.
In some circumstances, the Optimizer is able to create significantly better query plans if certain referential relationships have been defined between tables specified in the request. The Referential Constraint feature also referred to as soft referential integrity, permits you to take advantage of these optimizations without incurring the overhead of enforcing the suggested referential constraints.
The ADD option reserves additional partition numbers for a partitioning level to enable adding partitions to a partitioning level at a later time using an ALTER TABLE statement The following rules apply to the ADD clause for a row or column partition.
You can define the primary index for a table using either a PRIMARY KEY or UNIQUE constraint as the default primary index in a CREATE TABLE statement.
The following bullets list the rules for defining primary keys and UNIQUE constraints with respect to primary indexes:
You can still define a relationship for referential integrity by referencing the UPI of a table even if no primary key is defined explicitly for that table because it is always valid to define a referential integrity relationship with an alternate key.
The system defines this index as a NUPI by default except for the case of a single column table defined with the SET (no duplicate rows permitted) option, in which case the system defines it as a UPI.
1. If there is no PRIMARY INDEX, PRIMARY KEY constraint, or UNIQUE constraint defined in a CREATE TABLE statement, and the PrimaryIndexDefault parameter is set to N, then Teradata Database creates the table with no primary index.
2. Columns defined with either of the following constraints cannot be defined to be nullable.
3. Columns defined with any of the following constraints can be defined as nullable:
You should declare the column set that constitutes these index types to be NOT NULL unless there is a compelling reason not to.
Each queue table you define must stipulate the keyword QUEUE as 1 of the CREATE TABLE options following the table name; otherwise, the table you define does not have the properties associated with queue tables and you cannot use consume mode when you select from it (see SQL Data Manipulation Language).
The first column defined for any queue table must be a Queue Insertion Time Stamp (QITS) column. Each queue table has only 1 QITS column, and it must be defined exactly as indicated with the following attributes.
QITS_column_name TIMESTAMP(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6)
where QITS_column_name indicates the name you specify for the QITS column.
For REPLACE TRANSFORM:
A transition table is a dynamically created table that you can reference using a correlation name.
In the 2PC mode, DATABASE is treated as a DDL statement, so it is not valid.
There are various utilities available in Teradata. They are:
In Teradata, the FAST LOAD option loads a huge amount of data from a flat file into EMPTY tables.
There are many advantages of using the Teradata database, they are:
We can use the Teradata database in various ways, they are
The main components of Teradata Architecture are:
BYNET is the main component of Teradata architecture and it acts as a message-passing layer. BYNET decides which AMP should receive a message.
A Unique Primary Index (UPI) is unique and cannot have any duplicates. If you try and insert a row with a Primary Index value that is already in the table, the row will be rejected. A UPI enforces UNIQUENESS for a column.
The SQL syntax to create a Unique Primary Index is:
CREATE TABLE sample_1 (col_a INT ,col_b INT ,col_c INT) UNIQUE PRIMARY INDEX (col_b);
A Non-Unique Primary Index (NUPI) means that the values for the selected column can be non-unique. Duplicate values can exist.
The SQL syntax to create a Non-Unique Primary Index is:
CREATE TABLE sample_2 (col_x INT ,col_y INT ,col_z INT) PRIMARY INDEX (col_x);
The main purpose of a Columnar in a Teradata table is to spread the rows evenly across the AMPs.
Columnar example code:
CREATE Table Employee ( Emp_Id Integer ,Dept_Id Integer ,First_Name Varchar(20) ,Last_Name Char(20) ,Salary Decimal (10,2) ) No Primary Index PARTITION BY COLUMN;
In Teradata locking prevents multiple users from trying to access the same data simultaneously.
Locks can be applied at three levels:
Teradata contains four types of Locks, they are:
Teradata offers different types of data protection for databases. They are:
RAID, Cliques, Hot Standby Nodes, Fallback, Journaling, and Locks.
RAID stands for Redundant Array of Inexpensive Disks. RAID is a storage technology in Teradata that provides data protection at the disk drive level.
A clique is a group of nodes that share access to the same disk arrays. Each multi-node system has at least one clique.
Fallback is a feature of the Teradata Database, Fallback protects data in case of an AMP vproc failure. This protection can be done at the database or table level.
Ravindra Savaram is a Content Lead at Mindmajix.com. His passion lies in writing articles on the most popular IT platforms including Machine learning, DevOps, Data Science, Artificial Intelligence, RPA, Deep Learning, and so on. You can stay up to date on all these technologies by following him on LinkedIn and Twitter.