> ## Documentation Index
> Fetch the complete documentation index at: https://clickhouse.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# cast_* session settings

> ClickHouse session settings in the cast_* generated group.

export const SettingsInfoBlock = ({type, default_value, changeable_without_restart}) => {
  return <div className="not-prose" style={{
    display: "flex",
    flexWrap: "wrap",
    alignItems: "baseline",
    columnGap: "0.5rem",
    rowGap: "0.125rem",
    margin: "0.375rem 0",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <div style={{
    fontWeight: 600,
    opacity: 0.72
  }}>Type</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>Default</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          Changeable without restart
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

These settings are available in [system.settings](/docs/reference/system-tables/settings) and are autogenerated from [source](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp).

<h2 id="cast_ipv4_ipv6_default_on_conversion_error">
  cast\_ipv4\_ipv6\_default\_on\_conversion\_error
</h2>

<SettingsInfoBlock type="Bool" default_value="0" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "22.3"},{"label": "0"},{"label": "Make functions cast(value, 'IPv4') and cast(value, 'IPv6') behave same as toIPv4 and toIPv6 functions"}]}]} />

CAST operator into IPv4, CAST operator into IPV6 type, toIPv4, toIPv6 functions will return default value instead of throwing exception on conversion error.

<h2 id="cast_keep_nullable">
  cast\_keep\_nullable
</h2>

<SettingsInfoBlock type="Bool" default_value="0" />

Enables or disables keeping of the `Nullable` data type in [CAST](/docs/reference/functions/regular-functions/type-conversion-functions#CAST) operations.

When the setting is enabled and the argument of `CAST` function is `Nullable`, the result is also transformed to `Nullable` type. When the setting is disabled, the result always has the destination type exactly.

Possible values:

* 0 — The `CAST` result has exactly the destination type specified.
* 1 — If the argument type is `Nullable`, the `CAST` result is transformed to `Nullable(DestinationDataType)`.

**Examples**

The following query results in the destination data type exactly:

```sql theme={null}
SET cast_keep_nullable = 0;
SELECT CAST(toNullable(toInt32(0)) AS Int32) as x, toTypeName(x);
```

Result:

```text theme={null}
┌─x─┬─toTypeName(CAST(toNullable(toInt32(0)), 'Int32'))─┐
│ 0 │ Int32                                             │
└───┴───────────────────────────────────────────────────┘
```

The following query results in the `Nullable` modification on the destination data type:

```sql theme={null}
SET cast_keep_nullable = 1;
SELECT CAST(toNullable(toInt32(0)) AS Int32) as x, toTypeName(x);
```

Result:

```text theme={null}
┌─x─┬─toTypeName(CAST(toNullable(toInt32(0)), 'Int32'))─┐
│ 0 │ Nullable(Int32)                                   │
└───┴───────────────────────────────────────────────────┘
```

**See Also**

* [CAST](/docs/reference/functions/regular-functions/type-conversion-functions#CAST) functio