datafusion_expr/
table_source.rs

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14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18//! Table source
19
20use crate::{Expr, LogicalPlan};
21
22use arrow::datatypes::SchemaRef;
23use datafusion_common::{Constraints, Result};
24
25use std::{any::Any, borrow::Cow};
26
27/// Indicates how a filter expression is handled by
28/// [`TableProvider::scan`].
29///
30/// Filter expressions are boolean expressions used to reduce the number of
31/// rows that are read from a table. Only rows that evaluate to `true` ("pass
32/// the filter") are returned. Rows that evaluate to `false` or `NULL` are
33/// omitted.
34///
35/// [`TableProvider::scan`]: https://docs.rs/datafusion/latest/datafusion/datasource/provider/trait.TableProvider.html#tymethod.scan
36#[derive(Debug, Clone, PartialEq, Eq)]
37pub enum TableProviderFilterPushDown {
38    /// The filter cannot be used by the provider and will not be pushed down.
39    Unsupported,
40    /// The filter can be used, but the provider might still return some tuples
41    /// that do not pass the filter.
42    ///
43    /// In this case, DataFusion applies an additional `Filter` operation
44    /// after the scan to ensure all rows are filtered correctly.
45    Inexact,
46    /// The provider **guarantees** that it will omit **only** tuples which
47    /// pass the filter.
48    ///
49    /// In this case, DataFusion will not apply additional filtering.
50    Exact,
51}
52
53/// Indicates the type of this table for metadata/catalog purposes.
54#[derive(Debug, Clone, Copy, PartialEq, Eq)]
55pub enum TableType {
56    /// An ordinary physical table.
57    Base,
58    /// A non-materialized table that itself uses a query internally to provide data.
59    View,
60    /// A transient table.
61    Temporary,
62}
63
64impl std::fmt::Display for TableType {
65    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
66        match self {
67            TableType::Base => write!(f, "Base"),
68            TableType::View => write!(f, "View"),
69            TableType::Temporary => write!(f, "Temporary"),
70        }
71    }
72}
73
74/// Planning time information about a table.
75///
76/// This trait is used during logical query planning and optimizations, and
77/// provides a subset of the [`TableProvider`] trait, such as schema information
78/// and filter push-down capabilities. The [`TableProvider`] trait provides
79/// additional information needed for physical query execution, such as the
80/// ability to perform a scan or insert data.
81///
82/// # See Also:
83///
84/// [`DefaultTableSource`]  to go from [`TableProvider`], to `TableSource`
85///
86/// # Rationale
87///
88/// The reason for having two separate traits is to avoid having the logical
89/// plan code be dependent on the DataFusion execution engine. Some projects use
90/// DataFusion's logical plans and have their own execution engine.
91///
92/// [`TableProvider`]: https://docs.rs/datafusion/latest/datafusion/datasource/provider/trait.TableProvider.html
93/// [`DefaultTableSource`]: https://docs.rs/datafusion/latest/datafusion/datasource/default_table_source/struct.DefaultTableSource.html
94pub trait TableSource: Sync + Send {
95    fn as_any(&self) -> &dyn Any;
96
97    /// Get a reference to the schema for this table
98    fn schema(&self) -> SchemaRef;
99
100    /// Get primary key indices, if any
101    fn constraints(&self) -> Option<&Constraints> {
102        None
103    }
104
105    /// Get the type of this table for metadata/catalog purposes.
106    fn table_type(&self) -> TableType {
107        TableType::Base
108    }
109
110    /// Tests whether the table provider can make use of any or all filter expressions
111    /// to optimize data retrieval. Only non-volatile expressions are passed to this function.
112    fn supports_filters_pushdown(
113        &self,
114        filters: &[&Expr],
115    ) -> Result<Vec<TableProviderFilterPushDown>> {
116        Ok((0..filters.len())
117            .map(|_| TableProviderFilterPushDown::Unsupported)
118            .collect())
119    }
120
121    /// Get the Logical plan of this table provider, if available.
122    ///
123    /// For example, a view may have a logical plan, but a CSV file does not.
124    fn get_logical_plan(&self) -> Option<Cow<LogicalPlan>> {
125        None
126    }
127
128    /// Get the default value for a column, if available.
129    fn get_column_default(&self, _column: &str) -> Option<&Expr> {
130        None
131    }
132}
datafusion_expr/table_source.rs

datafusion_expr/
table_source.rs
