datafusion-expr 12.0.0

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//   http://www.apache.org/licenses/LICENSE-2.0
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use crate::Expr;
use arrow::datatypes::SchemaRef;
use std::any::Any;

///! Table source

/// Indicates whether and how a filter expression can be handled by a
/// TableProvider for table scans.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TableProviderFilterPushDown {
    /// The expression cannot be used by the provider.
    Unsupported,
    /// The expression can be used to help minimise the data retrieved,
    /// but the provider cannot guarantee that all returned tuples
    /// satisfy the filter. The Filter plan node containing this expression
    /// will be preserved.
    Inexact,
    /// The provider guarantees that all returned data satisfies this
    /// filter expression. The Filter plan node containing this expression
    /// will be removed.
    Exact,
}

/// Indicates the type of this table for metadata/catalog purposes.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TableType {
    /// An ordinary physical table.
    Base,
    /// A non-materialised table that itself uses a query internally to provide data.
    View,
    /// A transient table.
    Temporary,
}

/// The TableSource trait is used during logical query planning and optimizations and
/// provides access to schema information and filter push-down capabilities. This trait
/// provides a subset of the functionality of the TableProvider trait in the core
/// datafusion crate. The TableProvider trait provides additional capabilities needed for
/// physical query execution (such as the ability to perform a scan). The reason for
/// having two separate traits is to avoid having the logical plan code be dependent
/// on the DataFusion execution engine. Other projects may want to use DataFusion's
/// logical plans and have their own execution engine.
pub trait TableSource: Sync + Send {
    fn as_any(&self) -> &dyn Any;

    /// Get a reference to the schema for this table
    fn schema(&self) -> SchemaRef;

    /// Get the type of this table for metadata/catalog purposes.
    fn table_type(&self) -> TableType {
        TableType::Base
    }

    /// Tests whether the table provider can make use of a filter expression
    /// to optimise data retrieval.
    fn supports_filter_pushdown(
        &self,
        _filter: &Expr,
    ) -> datafusion_common::Result<TableProviderFilterPushDown> {
        Ok(TableProviderFilterPushDown::Unsupported)
    }
}