> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-fix-nav-issues.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Avoid nullable columns

> Why Nullable Columns should be avoided in ClickHouse

[`Nullable` column](/reference/data-types/nullable) (e.g. `Nullable(String)`) creates a separate column of `UInt8` type. This additional column has to be processed every time a user works with a Nullable column. This leads to additional storage space used and almost always negatively affects performance.

To avoid `Nullable` columns, consider setting a default value for that column.  For example, instead of:

```sql highlight={4} theme={null}
CREATE TABLE default.sample
(
    `x` Int8,
    `y` Nullable(Int8)
)
ENGINE = MergeTree
ORDER BY x
```

use

```sql highlight={4} theme={null}
CREATE TABLE default.sample2
(
    `x` Int8,
    `y` Int8 DEFAULT 0
)
ENGINE = MergeTree
ORDER BY x
```

Consider your use case; a default value may be inappropriate.