Hive Data Types

Dremio supports selecting the following Hive Database types. The following table shows the mappings from Hive to Dremio data types.

Note:
If a type is not present in the table, it is not currently supported.

Data Type Mappings

Complex Data Types

As of Dremio 4.3.0, Dremio supports the following complex data types:

• LIST: Supports extracting list elements using list indices.
• STRUCT: Supports extracting struct fields using field names within single quotes.
• UNION: Supports reading data from Union type field from Hive ORC tables.

Complex Data Type Mapping

Examples for LIST, STRUCT, and UNION

The following examples assume that the table, HiveOrcTable, exists in Hive and has the following structure:

HiveOrcTable Table Structure

LIST example

In this example, list_field is the column name whose data type is ARRAY in Hive:

SELECT list_field[0] from HiveOrcTable

STRUCT example

In this example, struct_field is the column name whose data type is STRUCT in Hive:

SELECT struct_field['field_name'] from HiveOrcTable

UNION example

In this example, union_field is the column name whose data type is UNIONTYPE in Hive:

SELECT union_field FROM HiveOrcTable

Implicit Type Casting for Parquet-formatted Files

Dremio implictly casts data types from Parquet-formatted files that differ from the defined schema of a Hive table. Each row in the table below represents the data type in a Parquet-formatted file, and the columns represent the data types defined in the schema of the Hive table. For example, if the data type of a named column in the Parquet file is INT and the data type of the column with the same name in the Hive table is either INT or BIGINT, Dremio will implicitly cast to that data type.

In addition, Dremio can implicitly cast VARCHAR to VARCHAR. However, this conversion is not enabled by default. To enable implicit casting of VARCHAR to VARCHAR, run the following command on the Hive table:

alter table <tableName> set enable_varchar_truncation=true

To disable implicit casting of VARCHAR to VARCHAR, run the following command on the Hive table:

alter table <tableName> set enable_varchar_truncation=false

Dremio applies the following rules for numerical conversions:

• Dremio returns null if a conversion results in overflow during runtime.
• Dremio truncates data and proceeds with a query if a conversion results in truncation.
• Dremio implicitly converts differences of precision, scale, and length for DECIMAL and VARCHAR data types.