Subchapter 4.35

Schema Types Minimize Bitwidth

rules/schema-types-minimize-bitwidth.mdMarkdown1 KBView on GitHub

Minimize Bit-Width for Numeric Types

Impact: HIGH

Select the smallest numeric type that accommodates your data range. Prefer unsigned types when negative values aren’t needed.

Incorrect (oversized types):

Schema Types Minimize Bitwidth · Clickhouse Best Practices · ClickHouse/agent-skills · Skills Docs

CREATE TABLE metrics (
    status_code Int64,        -- HTTP codes are 100-599
    age Int64,                -- Human age fits in UInt8
    year Int64,               -- Years fit in UInt16
    item_count Int64          -- Often small numbers
)

CREATE TABLE metrics (
    status_code UInt16,       -- 0-65,535 (HTTP codes fit easily)
    age UInt8,                -- 0-255 (sufficient for age)
    year UInt16,              -- 0-65,535 (sufficient for years)
    item_count UInt32         -- 0-4 billion (adjust based on actual max)
)

Type	Range	Bytes
UInt8	0 to 255	1
UInt16	0 to 65,535	2
UInt32	0 to 4.3 billion	4
UInt64	0 to 18 quintillion	8
Int8	-128 to 127	1
Int16	-32,768 to 32,767	2
Int32	-2.1 billion to 2.1 billion	4
Int64	-9 quintillion to 9 quintillion	8