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

# cast_string_* 会话设置

> cast_string_* 生成分组中的 ClickHouse 会话设置。

export const VersionHistory = ({rows = []}) => {
  if (rows.length === 0) {
    return null;
  }
  const headers = ["版本", "默认值", "注释"];
  const border = "1px solid rgba(128, 128, 128, 0.3)";
  const cell = {
    border,
    padding: "0.25rem 0.5rem",
    textAlign: "start",
    verticalAlign: "top"
  };
  return <details className="not-prose" style={{
    border,
    borderRadius: "0.5rem",
    margin: "0.5rem 0",
    padding: "0.5rem 0.75rem",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <summary style={{
    cursor: "pointer",
    fontWeight: 600,
    opacity: 0.72
  }}>
        版本历史
      </summary>
      <table style={{
    borderCollapse: "collapse",
    width: "100%",
    margin: "0.5rem 0 0"
  }}>
        <thead>
          <tr>
            {headers.map(header => <th key={header} style={{
    ...cell,
    fontWeight: 600,
    opacity: 0.72
  }}>
                {header}
              </th>)}
          </tr>
        </thead>
        <tbody>
          {rows.map((row, row_index) => <tr key={row.id ?? row_index}>
              {(row.items ?? []).map((item, item_index) => <td key={item_index} style={{
    ...cell,
    overflowWrap: "anywhere"
  }}>
                  {item?.label}
                </td>)}
            </tr>)}
        </tbody>
      </table>
    </details>;
};

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
  }}>类型</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>默认值</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          无需重启即可更改
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

这些设置可在 [system.settings](/zh/reference/system-tables/settings) 中查看，并根据 [源代码](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp) 自动生成。

<div id="cast_string_to_date_time_mode">
  ## cast\_string\_to\_date\_time\_mode
</div>

<SettingsInfoBlock type="DateTimeInputFormat" default_value="best_effort" />

允许在从 String 进行类型转换时，选择日期和时间文本表示的解析器。

可能的值：

* `'best_effort'` — 启用扩展解析。

  ClickHouse 可以解析基础的 `YYYY-MM-DD HH:MM:SS` 格式以及所有 [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) 日期和时间格式。例如，`'2018-06-08T01:02:03.000Z'`。

* `'best_effort_us'` — 与 `best_effort` 类似 (差异请参见 [parseDateTimeBestEffortUS](/zh/reference/functions/regular-functions/type-conversion-functions#parseDateTimeBestEffortUS))

* `'basic'` — 使用基础解析器。

  ClickHouse 只能解析基础的 `YYYY-MM-DD HH:MM:SS` 或 `YYYY-MM-DD` 格式。例如，`2019-08-20 10:18:56` 或 `2019-08-20`。

另请参见：

* [日期时间 数据类型。](/zh/reference/data-types/datetime)
* [处理日期和时间的函数。](/zh/reference/functions/regular-functions/date-time-functions)

<div id="cast_string_to_dynamic_use_inference">
  ## cast\_string\_to\_dynamic\_use\_inference
</div>

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

在将 String 转换为 Dynamic 时使用类型推断

<div id="cast_string_to_variant_use_inference">
  ## cast\_string\_to\_variant\_use\_inference
</div>

<SettingsInfoBlock type="Bool" default_value="1" />

在从 String 转换为 Variant 时使用类型推断。