diff --git a/rust/lancedb/src/error.rs b/rust/lancedb/src/error.rs index 6bd1ffa2b..be4641388 100644 --- a/rust/lancedb/src/error.rs +++ b/rust/lancedb/src/error.rs @@ -77,6 +77,8 @@ pub enum Error { ColumnAlreadyExists { name: String }, #[snafu(display("Column '{name}' is not a computed column"))] NotAComputedColumn { name: String }, + #[snafu(display("Table '{name}' is not a materialized view"))] + NotAMaterializedView { name: String }, #[snafu(display("Invalid expression for column '{column}': {message}"))] InvalidExpression { column: String, message: String }, diff --git a/rust/lancedb/src/lib.rs b/rust/lancedb/src/lib.rs index 70d023ccc..a5de41dfa 100644 --- a/rust/lancedb/src/lib.rs +++ b/rust/lancedb/src/lib.rs @@ -185,6 +185,7 @@ pub mod index; pub mod io; pub mod ipc; pub mod job; +pub mod materialized_view; #[cfg(feature = "metrics-otel")] pub mod metrics_otel; #[cfg(feature = "polars")] @@ -208,6 +209,7 @@ pub use error::{Error, JobFailure, Result}; pub use job::Job; use lance_index::vector::ApproxMode as LanceApproxMode; use lance_linalg::distance::DistanceType as LanceDistanceType; +pub use materialized_view::{MaterializedView, MaterializedViewDefinition}; /// Re-export of the [`metrics`](https://docs.rs/metrics) crate facade. Enable /// the `metrics` feature to publish LanceDB's internal metrics; install any /// `metrics`-compatible recorder to collect them. See also [`metrics_otel`] for diff --git a/rust/lancedb/src/materialized_view.rs b/rust/lancedb/src/materialized_view.rs new file mode 100644 index 000000000..686056931 --- /dev/null +++ b/rust/lancedb/src/materialized_view.rs @@ -0,0 +1,774 @@ +// SPDX-License-Identifier: Apache-2.0 +// SPDX-FileCopyrightText: Copyright The LanceDB Authors + +//! Materialized views. +//! +//! A materialized view is a normal table whose contents are defined by a query +//! over one source table -- projected expressions, an optional filter, an +//! optional row limit -- and maintained by refresh rather than by writes. +//! Creating one commits an empty table carrying the definition in schema +//! metadata; [`MaterializedView::refresh`] computes the rows. The source +//! table must have stable row ids ([`CreateMaterializedViewBuilder::execute`] +//! says why). +//! +//! The definition is tagged by kind so a variant added later reads back as a +//! view this version cannot refresh, not as a plain table. Only the projected +//! `select` form exists today. +//! +//! Because the view is a table, everything a table supports -- queries, +//! indexes, search -- works on it unchanged. Writes are not blocked, but a +//! refresh that rebuilds replaces them; the definition is the source of truth. + +use std::collections::HashMap; +use std::sync::Arc; + +use arrow_schema::{DataType, Field as ArrowField, Schema as ArrowSchema, SchemaRef}; +use lance_core::ROW_ID; +use lance_datafusion::planner::Planner; +use serde::{Deserialize, Serialize}; + +use crate::connection::Connection; +use crate::table::refresh::quote_identifier; +use crate::table::{Table, WriteOptions}; +use crate::{Error, Result}; + +/// Schema metadata key holding the view definition, as kind-tagged JSON. +pub const DEFINITION_META_KEY: &str = "mv.definition"; + +/// Schema metadata key holding the source table version the view was last +/// refreshed to. Absent until the first refresh. +pub const SOURCE_VERSION_META_KEY: &str = "mv.source_version"; + +/// Schema metadata key holding the wall-clock time of the last refresh, +/// in milliseconds since the epoch. +pub const REFRESHED_AT_MS_META_KEY: &str = "mv.refreshed_at_ms"; + +/// Column recording which source row produced each view row. +/// +/// Values are the source's stable `_rowid` at refresh time, valid across +/// source compactions, updates and deletes -- which is why a view's source +/// is required to keep stable row ids. +pub const SOURCE_ROW_ID_COLUMN: &str = "__source_row_id"; + +/// Value of the definition's `kind` tag for the projected `select` form. +pub const SELECT_KIND: &str = "select"; + +/// One projected output column of a view. +#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)] +pub struct ViewProjection { + /// Name of the column in the view. + pub output: String, + /// SQL expression over the source table that computes it. + pub expression: String, +} + +/// The query that defines a materialized view. +#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)] +pub struct MaterializedViewDefinition { + /// Name of the source table, in the same database as the view. + pub source_table: String, + /// The projected output columns, in view schema order. + pub projections: Vec, + /// SQL predicate selecting the source rows the view holds. + #[serde(default, skip_serializing_if = "Option::is_none")] + pub filter: Option, + /// Cap on the number of rows the view holds, in materialization order. + #[serde(default, skip_serializing_if = "Option::is_none")] + pub limit: Option, + /// Source columns the projections and filter read, derived at creation. + #[serde(default)] + pub inputs: Vec, +} + +/// A view definition as read back from schema metadata. +/// +/// Non-exhaustive: a kind added later is an additive change, and a caller that +/// only handles the kinds it knows keeps compiling. +#[derive(Debug, Clone, PartialEq, Eq)] +#[non_exhaustive] +pub enum MaterializedViewKind { + /// The projected `select` form. + Select(MaterializedViewDefinition), + /// A kind this version does not understand, written by a newer one. + /// + /// Reported rather than hidden so a caller can tell a view it cannot + /// refresh apart from a plain table. Nothing produces this. + Unrecognized { + /// The kind as it was found in the metadata. + kind: String, + }, +} + +/// Serialize `definition` into the kind-tagged form stored under +/// [`DEFINITION_META_KEY`]. +pub(crate) fn definition_to_metadata(definition: &MaterializedViewDefinition) -> Result { + let mut value = serde_json::to_value(definition).map_err(|e| Error::Runtime { + message: format!("failed to serialize view definition: {e}"), + })?; + value["kind"] = serde_json::Value::String(SELECT_KIND.to_string()); + Ok(value.to_string()) +} + +/// Read a view declaration off a schema metadata map, if it carries one. +/// +/// `Ok(None)` for a plain table. A present declaration that does not parse is +/// an error rather than `None`: the table was a view, and treating it as plain +/// would let it be silently rewritten. +pub fn materialized_view_kind( + metadata: &HashMap, +) -> Result> { + let Some(raw) = metadata.get(DEFINITION_META_KEY) else { + return Ok(None); + }; + let unreadable = |e: &dyn std::fmt::Display| Error::Runtime { + message: format!("unreadable materialized view definition: {e}"), + }; + let value: serde_json::Value = serde_json::from_str(raw).map_err(|e| unreadable(&e))?; + let kind = value + .get("kind") + .and_then(|k| k.as_str()) + .ok_or_else(|| unreadable(&"missing kind tag"))?; + if kind != SELECT_KIND { + return Ok(Some(MaterializedViewKind::Unrecognized { + kind: kind.to_string(), + })); + } + let definition = serde_json::from_value(value).map_err(|e| unreadable(&e))?; + Ok(Some(MaterializedViewKind::Select(definition))) +} + +/// Resolve a definition against the source schema into the view's projected +/// fields, with `inputs` filled in. +/// +/// Everything that can be known statically is checked here rather than at +/// refresh time: that each expression and the filter parse, that every column +/// they read exists, and that output names are free and unreserved. Empty +/// `projections` selects every source column, expanded against the schema as +/// it is now -- columns added to the source later are not picked up. +pub(crate) fn plan( + source_schema: SchemaRef, + source_table: &str, + projections: &[(String, String)], + filter: Option<&str>, + limit: Option, +) -> Result<(MaterializedViewDefinition, Vec)> { + let projections: Vec<(String, String)> = if projections.is_empty() { + source_schema + .fields() + .iter() + // A source that is itself a view carries its own provenance + // column; the new view records its own, not a copy. + .filter(|f| f.name() != SOURCE_ROW_ID_COLUMN) + .map(|f| (f.name().clone(), quote_identifier(f.name()))) + .collect() + } else { + projections.to_vec() + }; + + let planner = Planner::new(source_schema.clone()); + let mut fields = Vec::with_capacity(projections.len()); + let mut inputs = Vec::new(); + let mut declared: Vec<&str> = Vec::with_capacity(projections.len()); + + for (output, expression) in &projections { + if declared.contains(&output.as_str()) { + return Err(Error::ColumnAlreadyExists { + name: output.clone(), + }); + } + if output == SOURCE_ROW_ID_COLUMN || output == ROW_ID { + return Err(Error::InvalidInput { + message: format!("view column name '{output}' is reserved"), + }); + } + + let expr = planner + .parse_expr(expression) + .and_then(|expr| planner.optimize_expr(expr)) + .map_err(|e| Error::InvalidExpression { + column: output.clone(), + message: e.to_string(), + })?; + let expr_inputs = + resolve_inputs(&source_schema, &expr, |message| Error::InvalidExpression { + column: output.clone(), + message, + })?; + + // Physical expressions address columns by position, so the planner + // that types the expression is built on the projected schema. + let read_schema = project_schema(&source_schema, &expr_inputs); + let physical = Planner::new(read_schema.clone()) + .create_physical_expr(&expr) + .map_err(|e| Error::InvalidExpression { + column: output.clone(), + message: e.to_string(), + })?; + let data_type = + physical + .data_type(read_schema.as_ref()) + .map_err(|e| Error::InvalidExpression { + column: output.clone(), + message: e.to_string(), + })?; + + // Always nullable: what a refresh appends must fit the declared field + // whatever nullability the evaluator reports for a given batch. + fields.push(ArrowField::new(output, data_type, true)); + inputs.extend(expr_inputs); + declared.push(output); + } + + if let Some(filter) = filter { + let expr = planner + .parse_filter(filter) + .map_err(|e| Error::InvalidInput { + message: format!("invalid view filter: {e}"), + })?; + inputs.extend(resolve_inputs(&source_schema, &expr, |message| { + Error::InvalidInput { + message: format!("invalid view filter: {message}"), + } + })?); + } + + inputs.sort(); + inputs.dedup(); + + let definition = MaterializedViewDefinition { + source_table: source_table.to_string(), + projections: projections + .into_iter() + .map(|(output, expression)| ViewProjection { output, expression }) + .collect(), + filter: filter.map(String::from), + limit, + inputs, + }; + Ok((definition, fields)) +} + +/// The columns `expr` reads, each verified to exist in `schema`. +fn resolve_inputs( + schema: &ArrowSchema, + expr: &datafusion_expr::Expr, + error: impl Fn(String) -> Error, +) -> Result> { + let mut inputs = Planner::column_names_in_expr(expr); + inputs.sort(); + inputs.dedup(); + for input in &inputs { + if schema.field_with_name(input).is_err() { + return Err(error(format!("unknown column '{input}'"))); + } + } + Ok(inputs) +} + +fn project_schema(schema: &ArrowSchema, columns: &[String]) -> SchemaRef { + let fields: Vec = columns + .iter() + .filter_map(|name| schema.field_with_name(name).ok().cloned()) + .collect(); + Arc::new(ArrowSchema::new(fields)) +} + +/// Builds a materialized view. Created by +/// [`Connection::create_materialized_view`]. +pub struct CreateMaterializedViewBuilder { + connection: Connection, + name: String, + source: String, + projections: Vec<(String, String)>, + filter: Option, + limit: Option, +} + +impl CreateMaterializedViewBuilder { + pub(crate) fn new(connection: Connection, name: String, source: String) -> Self { + Self { + connection, + name, + source, + projections: Vec::new(), + filter: None, + limit: None, + } + } + + /// The view's columns, as `(name, SQL expression)` pairs. + /// + /// Not calling this selects every source column, expanded against the + /// source schema at creation time. + pub fn select( + mut self, + columns: impl IntoIterator, impl Into)>, + ) -> Self { + self.projections = columns + .into_iter() + .map(|(output, expression)| (output.into(), expression.into())) + .collect(); + self + } + + /// Only source rows matching the SQL predicate appear in the view. + pub fn only_if(mut self, filter: impl Into) -> Self { + self.filter = Some(filter.into()); + self + } + + /// Cap the view at `limit` rows, in materialization order. + pub fn limit(mut self, limit: u64) -> Self { + self.limit = Some(limit); + self + } + + /// Create the view: an empty table carrying the definition. No rows are + /// computed until a refresh. + /// + /// The source table must have stable row ids: they are what keeps the + /// view's provenance valid across source compactions, updates and + /// deletes, and they cannot be enabled after a table exists. + pub async fn execute(self) -> Result { + let source = self.connection.open_table(&self.source).execute().await?; + let Some(native) = source.as_native() else { + return Err(Error::NotSupported { + message: "materialized views are supported only on local databases".into(), + }); + }; + if !native.dataset.get().await?.manifest.uses_stable_row_ids() { + return Err(Error::InvalidInput { + message: format!( + "materialized views require stable row ids on the source table; \ + create '{}' with storage option new_table_enable_stable_row_ids=true", + self.source + ), + }); + } + let source_schema = source.schema().await?; + let (definition, mut fields) = plan( + source_schema, + &self.source, + &self.projections, + self.filter.as_deref(), + self.limit, + )?; + fields.push(ArrowField::new( + SOURCE_ROW_ID_COLUMN, + DataType::UInt64, + false, + )); + + let metadata = HashMap::from([( + DEFINITION_META_KEY.to_string(), + definition_to_metadata(&definition)?, + )]); + let schema = Arc::new(ArrowSchema::new_with_metadata(fields, metadata)); + // Stable row ids so the view can itself source another view. + let table = self + .connection + .create_empty_table(&self.name, schema) + .write_options(WriteOptions { + lance_write_params: Some(lance::dataset::WriteParams { + enable_stable_row_ids: true, + ..Default::default() + }), + }) + .execute() + .await?; + Ok(MaterializedView { table, definition }) + } +} + +/// A handle on a materialized view: the view table plus its parsed definition. +#[derive(Debug, Clone)] +pub struct MaterializedView { + table: Table, + definition: MaterializedViewDefinition, +} + +impl MaterializedView { + /// Interpret `table` as a materialized view. + /// + /// Fails with [`Error::NotAMaterializedView`] for a plain table and + /// [`Error::NotSupported`] for a view whose kind this version cannot + /// refresh. + pub async fn from_table(table: Table) -> Result { + let schema = table.schema().await?; + match materialized_view_kind(schema.metadata())? { + Some(MaterializedViewKind::Select(definition)) => Ok(Self { table, definition }), + Some(MaterializedViewKind::Unrecognized { kind }) => Err(Error::NotSupported { + message: format!( + "materialized view '{}' is defined by '{kind}', which this version of \ + lancedb cannot refresh", + table.name() + ), + }), + None => Err(Error::NotAMaterializedView { + name: table.name().to_string(), + }), + } + } + + /// The view, as the table it is. Queries, indexes and search all apply. + pub fn table(&self) -> &Table { + &self.table + } + + pub fn name(&self) -> &str { + self.table.name() + } + + /// The query that defines the view. + pub fn definition(&self) -> &MaterializedViewDefinition { + &self.definition + } +} + +impl Connection { + /// Define a materialized view named `name` over `source`. + /// + /// The view is created empty, with the definition recorded in its schema + /// metadata; refresh computes the rows. Local databases only. + /// + /// ```no_run + /// # use lancedb::Connection; + /// # async fn create(conn: &Connection) -> Result<(), Box> { + /// let view = conn + /// .create_materialized_view("loud_adults", "people") + /// .select([("name", "upper(name)"), ("age", "age")]) + /// .only_if("age >= 18") + /// .execute() + /// .await?; + /// println!("{}", view.definition().source_table); + /// # Ok(()) + /// # } + /// ``` + pub fn create_materialized_view( + &self, + name: impl Into, + source: impl Into, + ) -> CreateMaterializedViewBuilder { + CreateMaterializedViewBuilder::new(self.clone(), name.into(), source.into()) + } + + /// Open the materialized view named `name`. + pub async fn open_materialized_view( + &self, + name: impl Into, + ) -> Result { + let table = self.open_table(name).execute().await?; + MaterializedView::from_table(table).await + } + + /// The materialized views in this database. + /// + /// Reads every table's schema to find them, so this costs an open per + /// table. A table that cannot be opened is skipped rather than failing + /// the listing. + pub async fn list_materialized_views(&self) -> Result> { + let names = self.table_names().execute().await?; + let mut views = Vec::new(); + for name in names { + let Ok(table) = self.open_table(&name).execute().await else { + continue; + }; + let schema = table.schema().await?; + if let Some(MaterializedViewKind::Select(definition)) = + materialized_view_kind(schema.metadata())? + { + views.push(MaterializedView { table, definition }); + } + } + Ok(views) + } +} + +#[cfg(test)] +mod tests { + use arrow_array::record_batch; + + use super::*; + use crate::connect; + + async fn people_db() -> Connection { + let conn = connect("memory://").execute().await.unwrap(); + let batch = record_batch!( + ("name", Utf8, ["ada", "grace", "alan"]), + ("age", Int32, [36, 85, 41]) + ) + .unwrap(); + conn.create_table("people", batch) + .write_options(stable_row_ids()) + .execute() + .await + .unwrap(); + conn + } + + /// Sources must keep stable row ids; see the create-time gate. + pub(super) fn stable_row_ids() -> WriteOptions { + WriteOptions { + lance_write_params: Some(lance::dataset::WriteParams { + enable_stable_row_ids: true, + ..Default::default() + }), + } + } + + #[tokio::test] + async fn test_create_records_the_definition() { + let conn = people_db().await; + let view = conn + .create_materialized_view("adults", "people") + .select([("name", "name"), ("shout", "upper(name)")]) + .only_if("age >= 18") + .limit(10) + .execute() + .await + .unwrap(); + + assert_eq!(view.name(), "adults"); + assert_eq!( + view.definition(), + &MaterializedViewDefinition { + source_table: "people".into(), + projections: vec![ + ViewProjection { + output: "name".into(), + expression: "name".into() + }, + ViewProjection { + output: "shout".into(), + expression: "upper(name)".into() + }, + ], + filter: Some("age >= 18".into()), + limit: Some(10), + inputs: vec!["age".into(), "name".into()], + } + ); + + // The definition round-trips off the stored schema, not the handle. + let reopened = conn.open_materialized_view("adults").await.unwrap(); + assert_eq!(reopened.definition(), view.definition()); + } + + #[tokio::test] + async fn test_view_schema_is_derived_from_the_query() { + let conn = people_db().await; + let view = conn + .create_materialized_view("shapes", "people") + .select([("shout", "upper(name)"), ("next_age", "age + 1")]) + .execute() + .await + .unwrap(); + + let schema = view.table().schema().await.unwrap(); + assert_eq!( + schema.field_with_name("shout").unwrap().data_type(), + &DataType::Utf8 + ); + assert_eq!( + schema.field_with_name("next_age").unwrap().data_type(), + &DataType::Int32 + ); + assert_eq!( + schema + .field_with_name(SOURCE_ROW_ID_COLUMN) + .unwrap() + .data_type(), + &DataType::UInt64 + ); + assert_eq!(view.table().count_rows(None).await.unwrap(), 0); + } + + /// No projection selects every source column, expanded now: the schema + /// captured at creation is the definition. + #[tokio::test] + async fn test_default_projection_captures_the_source_schema() { + let conn = people_db().await; + let view = conn + .create_materialized_view("copy", "people") + .execute() + .await + .unwrap(); + assert_eq!( + view.definition() + .projections + .iter() + .map(|p| p.output.as_str()) + .collect::>(), + vec!["name", "age"] + ); + assert_eq!(view.definition().inputs, vec!["age", "name"]); + } + + #[tokio::test] + async fn test_unknown_column_fails_at_create_time() { + let conn = people_db().await; + let err = conn + .create_materialized_view("bad", "people") + .select([("x", "missing + 1")]) + .execute() + .await + .unwrap_err(); + assert!(matches!(err, Error::InvalidExpression { column, .. } if column == "x")); + assert!( + !conn + .table_names() + .execute() + .await + .unwrap() + .contains(&"bad".to_string()) + ); + } + + #[tokio::test] + async fn test_unknown_filter_column_fails_at_create_time() { + let conn = people_db().await; + let err = conn + .create_materialized_view("bad", "people") + .only_if("missing > 1") + .execute() + .await + .unwrap_err(); + assert!(matches!(err, Error::InvalidInput { message } if message.contains("missing"))); + } + + #[tokio::test] + async fn test_duplicate_output_is_rejected() { + let conn = people_db().await; + let err = conn + .create_materialized_view("bad", "people") + .select([("dup", "age"), ("dup", "age + 1")]) + .execute() + .await + .unwrap_err(); + assert!(matches!(err, Error::ColumnAlreadyExists { name } if name == "dup")); + } + + #[tokio::test] + async fn test_reserved_output_name_is_rejected() { + let conn = people_db().await; + let err = conn + .create_materialized_view("bad", "people") + .select([(SOURCE_ROW_ID_COLUMN, "age")]) + .execute() + .await + .unwrap_err(); + assert!(matches!(err, Error::InvalidInput { message } if message.contains("reserved"))); + } + + #[tokio::test] + async fn test_missing_source_fails() { + let conn = connect("memory://").execute().await.unwrap(); + let err = conn + .create_materialized_view("v", "nope") + .execute() + .await + .unwrap_err(); + assert!(matches!(err, Error::TableNotFound { .. })); + } + + /// Provenance has to survive source compactions and updates, and stable + /// row ids cannot be enabled after a table exists -- so the requirement + /// is checked at the last moment the caller can still act on it. + #[tokio::test] + async fn test_source_without_stable_row_ids_is_refused() { + let conn = connect("memory://").execute().await.unwrap(); + let batch = record_batch!(("x", Int32, [1, 2])).unwrap(); + conn.create_table("plain", batch).execute().await.unwrap(); + + let err = conn + .create_materialized_view("v", "plain") + .execute() + .await + .unwrap_err(); + assert!( + matches!(err, Error::InvalidInput { message } if message.contains("stable row ids")) + ); + assert!( + !conn + .table_names() + .execute() + .await + .unwrap() + .contains(&"v".to_string()) + ); + } + + #[tokio::test] + async fn test_name_collision_fails() { + let conn = people_db().await; + let err = conn + .create_materialized_view("people", "people") + .execute() + .await + .unwrap_err(); + assert!(matches!(err, Error::TableAlreadyExists { .. })); + } + + #[tokio::test] + async fn test_a_plain_table_is_not_a_view() { + let conn = people_db().await; + let table = conn.open_table("people").execute().await.unwrap(); + let err = MaterializedView::from_table(table).await.unwrap_err(); + assert!(matches!(err, Error::NotAMaterializedView { name } if name == "people")); + + let err = conn.open_materialized_view("people").await.unwrap_err(); + assert!(matches!(err, Error::NotAMaterializedView { .. })); + } + + /// The reason the kind is tagged: a definition written by a newer version + /// reads back as a view this one cannot refresh, not as a plain table. + #[tokio::test] + async fn test_unrecognized_kind_is_refused_by_name() { + let conn = people_db().await; + conn.create_materialized_view("v", "people") + .execute() + .await + .unwrap(); + let table = conn.open_table("v").execute().await.unwrap(); + table + .as_native() + .unwrap() + .replace_schema_metadata(HashMap::from([( + DEFINITION_META_KEY.to_string(), + r#"{"kind": "join"}"#.to_string(), + )])) + .await + .unwrap(); + + let err = conn.open_materialized_view("v").await.unwrap_err(); + assert!(matches!(err, Error::NotSupported { message } if message.contains("join"))); + } + + #[tokio::test] + async fn test_list_reports_views_and_only_views() { + let conn = people_db().await; + conn.create_materialized_view("adults", "people") + .only_if("age >= 18") + .execute() + .await + .unwrap(); + + let views = conn.list_materialized_views().await.unwrap(); + assert_eq!( + views.iter().map(|v| v.name()).collect::>(), + vec!["adults"] + ); + assert_eq!(views[0].definition().filter.as_deref(), Some("age >= 18")); + } + + #[tokio::test] + async fn test_drop_is_drop_table() { + let conn = people_db().await; + conn.create_materialized_view("v", "people") + .execute() + .await + .unwrap(); + conn.drop_table("v", &[]).await.unwrap(); + assert!(conn.list_materialized_views().await.unwrap().is_empty()); + } +} diff --git a/rust/lancedb/src/table/refresh.rs b/rust/lancedb/src/table/refresh.rs index 74c30a602..660dd4064 100644 --- a/rust/lancedb/src/table/refresh.rs +++ b/rust/lancedb/src/table/refresh.rs @@ -136,7 +136,7 @@ fn declared_expression(dataset: &Dataset, column: &str) -> Result { /// /// Lance's dialect delimits with backticks, so a double-quoted name would /// parse as a string literal rather than a column. -fn quote_identifier(name: &str) -> String { +pub(crate) fn quote_identifier(name: &str) -> String { format!("`{}`", name.replace('`', "``")) }