> ## 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.

# optimize_if_* 会话设置

> ClickHouse 中 optimize_if_* 生成组的会话设置。

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](/docs/zh/reference/system-tables/settings) 中查看，并由 [源代码](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp) 自动生成。

<div id="optimize_if_chain_to_multiif">
  ## optimize\_if\_chain\_to\_multiif
</div>

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

将 `if(cond1, then1, if(cond2, ...))` 链替换为 multiIf。当前这对数值类型没有益处。

<div id="optimize_if_transform_strings_to_enum">
  ## optimize\_if\_transform\_strings\_to\_enum
</div>

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

将 If 和 Transform 中的 String 类型参数替换为枚举类型。默认禁用，因为这可能会在分布式查询中产生不一致的更改，进而导致查询失败。