What is the difference between hive view and a hive external table When should it be used ?

Editor — Tue, 13 Jul 2021 22:18:46 +0000

Difference between hive view and a hive external table When should it be used

A view is a query which is defined as a table.

For example:

CREATE VIEW x AS SELECT * FROM y;

When the user queries table x the query planner combines the queries and executes a single one.

This is something like

SELECT * FROM x;

is translated to

SELECT * FROM y;
Then:

DROP TABLE abc;
If the table is defined as external:

CREATE EXTERNAL table abc (….);

An external table is something totally different. An external TABLE is a table that when DROPPED will NOT remove the physical data.
This is a alternative that affects how data is loaded, controlled, and managed.

Use EXTERNAL tables:

The data is also used outside of Hive.
For example, the data files are browse and processed by an existing program that doesn’t lock the files.
Data needs to stay within the underlying location even after a DROP TABLE.
Pointing multiple patterns at a single data it sets repeats via possible patterns.User can use custom location like ASV.
Hive does not contain own data and control settings, dirs, etc.In Hive existing table (i.e) not modify.

Use INTERNAL tables:

Temporary data needs Hive to manage the table and data.

What is the difference between a normal hive table and hive table stored as ORC ?

Editor — Tue, 13 Jul 2021 21:51:40 +0000

Difference between a normal hive table and hive table stored as ORC

Normal hive table	Hive table stored as orc
Hive data is organized into Databases: Namespaces function to avoid naming conflicts for tables, views, partitions, columns, and so on.	It produce efficient way to store Hive data.It designed to overcome the drawback of others Hive file formats Using Optimized Row Columnar files improves speed when Hive is reading, writing, and processing data.
Databases can also be used to enforce security for a user or group of users.	Advantages- Single file as the output of each task, that reduces the NameNode’s load.
There are two types of tables in Hive, one is Managed table and second is external table. The difference is, when you drop a table, if it is managed table hive deletes both data and meta data, if it is external table Hive only deletes metadata.	An Optimized Row Columnar file contains types of data define as stripes,along with information in a file footer. At the end of the file a postscript holds compression parameters and the size of the compressed footer.
It damage how data is loaded, controlled, and managed in Hive ;By use external tables when the data is also used outside of Hive.	Default stripe size is 250 MB. large stripe sizes enable large, efficient reads from HDFS.
The data files are read and processed by an existing program that doesn’t lock the files. Data needs to remain in the underlying location even after a DROP	File footer having a list of stripes and number of rows,each columns contains count, min, max, and sum.
Storing data in Hive is nothing but storing data in HDFS (Hadoop).	The stripe file footer contains a directory of stream locations.Row data is used in table scans

managed table vs external table in hive - Wikitechy

What is the difference between hive view and a hive external table When should it be used ?

Difference between hive view and a hive external table When should it be used

Use EXTERNAL tables:

Use INTERNAL tables:

What is the difference between a normal hive table and hive table stored as ORC ?

Difference between a normal hive table and hive table stored as ORC