> ## 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.

# enable_optimize_predicate_expression_* session settings

> ClickHouse session settings in the enable_optimize_predicate_expression_* 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="enable_optimize_predicate_expression">
  enable\_optimize\_predicate\_expression
</h2>

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

<VersionHistory rows={[{"id": "row-1","items": [{"label": "18.12.17"},{"label": "1"},{"label": "Optimize predicates to subqueries by default"}]}]} />

Turns on predicate pushdown in `SELECT` queries.

Predicate pushdown may significantly reduce network traffic for distributed queries.

Possible values:

* 0 — Disabled.
* 1 — Enabled.

Usage

Consider the following queries:

1. `SELECT count() FROM test_table WHERE date = '2018-10-10'`
2. `SELECT count() FROM (SELECT * FROM test_table) WHERE date = '2018-10-10'`

If `enable_optimize_predicate_expression = 1`, then the execution time of these queries is equal because ClickHouse applies `WHERE` to the subquery when processing it.

If `enable_optimize_predicate_expression = 0`, then the execution time of the second query is much longer because the `WHERE` clause applies to all the data after the subquery finishes.

<h2 id="enable_optimize_predicate_expression_to_final_subquery">
  enable\_optimize\_predicate\_expression\_to\_final\_subquery
</h2>

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

Allow push predicate to final subquery.