> ## 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.

# external_table_* session settings

> ClickHouse session settings in the external_table_* 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="external_table_functions_use_nulls">
  external\_table\_functions\_use\_nulls
</h2>

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

Defines how [mysql](/docs/reference/functions/table-functions/mysql), [postgresql](/docs/reference/functions/table-functions/postgresql) and [odbc](/docs/reference/functions/table-functions/odbc) table functions use Nullable columns.

Possible values:

* 0 — The table function explicitly uses Nullable columns.
* 1 — The table function implicitly uses Nullable columns.

**Usage**

If the setting is set to `0`, the table function does not make Nullable columns and inserts default values instead of NULL. This is also applicable for NULL values inside arrays.

<h2 id="external_table_strict_query">
  external\_table\_strict\_query
</h2>

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

If it is set to true, transforming expression to local filter is forbidden for queries to external tables.