fuse_encoding.md

title	FUSE_ENCODING

import FunctionDescription from '@site/src/components/FunctionDescription';

Returns the encoding types applied to a specific column within a table. It helps you understand how data is compressed and stored in a native format within the table.

Syntax

FUSE_ENCODING('<database_name>', '<table_name>', '<column_name>')

The function returns a result set with the following columns:

Column	Data Type	Description
VALIDITY_SIZE	Nullable(UInt32)	The size of a bitmap value that indicates whether each row in the column has a non-null value. This bitmap is used to track the presence or absence of null values in the column's data.
COMPRESSED_SIZE	UInt32	The size of the column data after compression.
UNCOMPRESSED_SIZE	UInt32	The size of the column data before applying encoding.
LEVEL_ONE	String	The primary or initial encoding applied to the column.
LEVEL_TWO	Nullable(String)	A secondary or recursive encoding method applied to the column after the initial encoding.

Examples

-- Create a table with an integer column 'c' and apply 'Lz4' compression
CREATE TABLE t(c INT) STORAGE_FORMAT = 'native' COMPRESSION = 'lz4';

-- Insert data into the table.
INSERT INTO t SELECT number FROM numbers(2048);

-- Analyze the encoding for column 'c' in table 't'
SELECT LEVEL_ONE, LEVEL_TWO, COUNT(*) 
FROM FUSE_ENCODING('default', 't', 'c') 
GROUP BY LEVEL_ONE, LEVEL_TWO;

level_one   |level_two|count(*)|
------------+---------+--------+
DeltaBitpack|         |       1|

--  Insert 2,048 rows with the value 1 into the table 't'
INSERT INTO t (c)
SELECT 1
FROM numbers(2048);

SELECT LEVEL_ONE, LEVEL_TWO, COUNT(*) 
FROM FUSE_ENCODING('default', 't', 'c') 
GROUP BY LEVEL_ONE, LEVEL_TWO;

level_one   |level_two|count(*)|
------------+---------+--------+
OneValue    |         |       1|
DeltaBitpack|         |       1|