Can we truncate a table in Hive?

The TRUNCATE command removes all rows from the table as well as from the partition, but keeps the table structure as it is. Truncating a table in Hive is indirectly removing the files from the HDFS as a table in Hive is just a way of reading the data from the HDFS in the table or structural format.

How do I truncate a partitioned Hive table?

Use the ALTER TABLEā€¦ TRUNCATE PARTITION command to remove the data from the specified partition, leaving the partition structure intact. When you truncate a partition, any subpartitions of that partition are also truncated.

What is the truncate table?

Removes all rows from a table or specified partitions of a table, without logging the individual row deletions. TRUNCATE TABLE is similar to the DELETE statement with no WHERE clause; however, TRUNCATE TABLE is faster and uses fewer system and transaction log resources.

Can we delete data from Hive table?

Apache Hive is not designed for online transaction processing and does not offer real-time queries and row level updates and deletes. To use ACID transaction, one must create a table with ACID transaction properties set. Delete can be performed on the table that supports ACID.

How do I truncate an external table?

You cannot delete or truncate an external table. However, you can alter and drop the table definition. Dropping an external table drops the table definition, but it does not delete the data file that is associated with the table. To drop an external table, use the DROP statement.

What is difference between truncate and delete command?

Key differences between DELETE and TRUNCATE The DELETE statement is used when we want to remove some or all of the records from the table, while the TRUNCATE statement will delete entire rows from a table. DELETE is a DML command as it only modifies the table data, whereas the TRUNCATE is a DDL command.

Why use TRUNCATE instead of delete?

Truncate removes all records and doesn’t fire triggers. Truncate is faster compared to delete as it makes less use of the transaction log. Truncate is not possible when a table is referenced by a Foreign Key or tables are used in replication or with indexed views.

How long does it take to TRUNCATE a table?

1 Answer. A millisecond or so. Truncate is O(1) – a pure metadata operation. This is assuming there is no concurrent activity on the table.

How would you delete the data of Hive table without deleting the table?

The goal is to destroy a Hive schema but keep the data underneath. Given a Hive external table, created for example with script 1, it can be dropped with script 2. This deletes the data (removes the folder /user/me/data/ ).

How do I remove duplicates from Hive table?

To remove duplicate values, you can use insert overwrite table in Hive using the DISTINCT keyword while selecting from the original table. The DISTINCT keyword returns unique records from the table.

How do you truncate a table in Databricks?

Removes all the rows from a table or partition(s). The table must not be a view or an external or temporary table. In order to truncate multiple partitions at once, specify the partitions in partition_spec .

How are tables stored in hive?

Tables are stored in the form of directories. Whenever you are creating a table, the table structure is stored in hive metastore. Metastore is a kind of database which is used to store the table details like column name, datatype, partition, bucketing etc.

How to delete the hive table data?

How to delete hive tables using datastep Create a hive table using SAS data step and note the no of rows. Drop the table using proc sql delete / proc dataset delete. Run the create table step again. Count the number of rows.

What is external table in hive?

An external table describes the metadata / schema on external files. External table files can be accessed and managed by processes outside of Hive. External tables can access data stored in sources such as Azure Storage Volumes (ASV) or remote HDFS locations.

Can we truncate external tables?

You can truncate any table, including tables that are referenced in foreign-key constraints. You don’t need to vacuum a table after truncating it. The TRUNCATE command commits the transaction in which it is run; therefore, you can’t roll back a TRUNCATE operation, and a TRUNCATE command may commit other operations when it commits itself.