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Add SQL projection aliases and literal expressions support

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This commit is contained in:
Hassan Abedi 2026-04-09 12:50:06 +02:00
parent dd7b16ce93
commit 23cbc6a4bf
20 changed files with 374 additions and 55 deletions
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10
Makefile
View File

@ -77,7 +77,7 @@ install-deps: ## Install development dependencies
.PHONY: lint
lint: format ## Run the linters
@echo "Linting Rust files..."
@DEBUG_PROJ=$(DEBUG_PROJ) cargo clippy -- -D warnings -D clippy::unwrap_used -D clippy::expect_used
@DEBUG_PROJ=$(DEBUG_PROJ) cargo clippy --all-targets --all-features -- -D warnings
.PHONY: audit
audit: ## Run security audit on Rust dependencies
@ -92,7 +92,7 @@ docs: format ## Generate the documentation
.PHONY: fix-lint
fix-lint: ## Fix the linter warnings
@echo "Fixing linter warnings..."
@cargo clippy --fix --allow-dirty --allow-staged --all-targets --workspace
@cargo clippy --fix --allow-dirty --allow-staged --all-targets --all-features -- -D warnings
.PHONY: nextest
nextest: ## Run tests using nextest
@ -116,5 +116,9 @@ test-hooks: ## Test Git hooks on all files
@pre-commit run --all-files --show-diff-on-failure
.PHONY: check
check: format lint test ## Run format, lint, and test
check: format ## Run format, lint, and test
@echo "Checking formatting..."
@cargo fmt --check
@$(MAKE) lint
@$(MAKE) test
@echo "All checks passed."

35
README.md
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@ -2,10 +2,10 @@
An experimental Rust project for building query-engine components.
Right now the repository is centered on a chase-based reasoning core plus a
small interactive frontend, plus an early relational/SQL scaffold. The broader
target shape is a query engine with clearer front-end, planning, optimization,
and execution boundaries.
Right now the repository is centered on a chase-based reasoning core, a small
interactive frontend, and an early relational/SQL scaffold. The broader target
shape is a query engine with clearer front-end, planning, optimization, and
execution boundaries.
### Current scope
@ -16,6 +16,22 @@ and execution boundaries.
- Relational schema, catalog, logical-plan, and execution scaffolding
- A minimal SQL slice for single-table `SELECT-FROM-WHERE` queries
### Architecture
The repository is currently organized around a few clear subsystems:
- `src/chase/`: rule-engine data structures and chase execution
- `src/frontend/`: REPL, script, GUI, and explanation rendering
- `src/relational/`: schemas, values, rows, and result sets
- `src/catalog/`: predicate-backed table metadata
- `src/sql/`: minimal SQL AST and parser
- `src/planner/`: logical plan structures and SQL-to-plan translation
- `src/execution/`: execution for the current logical-plan subset
Today, the chase subsystem is still the most mature part of the codebase. The
relational and SQL modules are present to create clean extension points for a
broader query-engine architecture.
### Intended Direction
The medium-term direction is to evolve this project into a more general
@ -75,6 +91,7 @@ cargo run -- script examples/scripts/ancestor.chase
```text
fact Parent(alice, bob).
rule Parent(?X, ?Y) -> Ancestor(?X, ?Y).
sql SELECT * FROM Parent;
run.
query Ancestor(?X, ?Y)?
explain Ancestor(alice, carol)?
@ -100,6 +117,14 @@ Currently supported examples:
SELECT * FROM Parent
SELECT c0 FROM Parent
SELECT c0 FROM Parent WHERE c1 = 'bob'
SELECT c0 AS parent_name, 'seed' AS label FROM Parent
```
In the REPL or script runner, use the `sql` command and end the statement with
`;`:
```text
sql SELECT c0 FROM Parent WHERE c1 = 'bob';
```
Current limits:
@ -108,7 +133,7 @@ Current limits:
- positional column names such as `c0`, `c1`
- no joins
- no aggregates
- no aliases
- projection aliases only via `AS`
### Development

3
examples/geolog/README.md
View File

@ -3,6 +3,9 @@
This directory contains example `.geolog` files that use a richer DSL than the
minimal `.chase` script language in `examples/scripts/`.
These files are reference material and experiments. They are not currently
wired into the `query-engine` binary, REPL, SQL parser, or planner pipeline.
This README summarizes the Geolog DSL structure as it appears in the examples in
this directory. It should be read as a practical, example-driven reference, not
as a formal or complete language specification.

1
examples/scripts/README.md
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@ -4,6 +4,7 @@ These scripts can be executed with:
```bash
make script SCRIPT=examples/scripts/ancestor.chase
cargo run -- script examples/scripts/ancestor.chase
```
Available examples:

2
flake.nix
View File

@ -1,5 +1,5 @@
{
description = "A playground for experimenting with query engine stuff";
description = "A playground for experimenting with query engine components in Rust";
inputs = {
nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

14
src/catalog/mod.rs
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@ -1,4 +1,7 @@
//! Minimal catalog support for mapping predicates to relational schemas.
//!
//! The current catalog is intentionally lightweight. It infers table schemas
//! from predicate arities and null occurrences in an [`Instance`](crate::chase::Instance).
use std::collections::HashMap;
use std::error::Error;
@ -7,9 +10,12 @@ use std::fmt;
use crate::chase::{Instance, Term};
use crate::relational::{DataType, Field, Schema};
/// Errors returned by the predicate-backed catalog.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum CatalogError {
/// The requested predicate-backed table does not exist.
UnknownTable(String),
/// Facts for one predicate do not all have the same arity.
InconsistentArity {
table: String,
expected: usize,
@ -36,26 +42,34 @@ impl fmt::Display for CatalogError {
impl Error for CatalogError {}
/// A minimal catalog that maps predicate names to inferred relational schemas.
#[derive(Debug, Clone, Default)]
pub struct PredicateCatalog {
schemas: HashMap<String, Schema>,
}
impl PredicateCatalog {
/// Create an empty catalog.
pub fn new() -> Self {
Self::default()
}
/// Register a table schema explicitly.
pub fn register_table(&mut self, table: impl Into<String>, schema: Schema) {
self.schemas.insert(table.into(), schema);
}
/// Fetch a schema for a table name.
pub fn schema_for(&self, table: &str) -> Result<&Schema, CatalogError> {
self.schemas
.get(table)
.ok_or_else(|| CatalogError::UnknownTable(table.to_string()))
}
/// Infer table schemas from the predicates present in an instance.
///
/// Each predicate becomes one table, with positional column names `c0`,
/// `c1`, and so on.
pub fn from_instance(instance: &Instance) -> Result<Self, CatalogError> {
let mut arities = HashMap::new();
let mut nullable_positions: HashMap<String, Vec<bool>> = HashMap::new();

4
src/execution/mod.rs
View File

@ -7,9 +7,12 @@ use crate::chase::{Instance, Term};
use crate::planner::logical::{LogicalExpr, LogicalPlan};
use crate::relational::{ResultSet, Row, Value};
/// Errors returned by the current logical-plan executor.
#[derive(Debug)]
pub enum ExecutionError {
/// A column reference could not be resolved.
UnknownColumn(String),
/// The scan layer encountered a variable term where a ground value was expected.
NonGroundScanTerm,
}
@ -26,6 +29,7 @@ impl fmt::Display for ExecutionError {
impl Error for ExecutionError {}
/// Execute the current logical-plan subset against an instance-backed source.
pub fn execute(plan: &LogicalPlan, instance: &Instance) -> Result<ResultSet, ExecutionError> {
match plan {
LogicalPlan::Scan { table, schema } => {

20
src/frontend/language.rs
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@ -2,11 +2,14 @@
use crate::chase::rule::RuleBuilder;
use crate::chase::{Atom, Rule, Term};
use crate::sql::ast::Select;
use crate::sql::parser::parse_select;
#[derive(Debug, Clone)]
pub enum Command {
Fact(Atom),
Rule(Rule),
Sql(Select),
Run,
Query(Vec<Atom>),
Explain(Vec<Atom>),
@ -51,6 +54,11 @@ pub fn parse_command(input: &str) -> Result<Command, String> {
return Ok(Command::Help);
}
if let Some(rest) = strip_keyword(trimmed, "sql") {
let select = parse_select(trim_suffix(rest, ';')?).map_err(|err| err.to_string())?;
return Ok(Command::Sql(select));
}
if let Some(rest) = strip_keyword(trimmed, "fact") {
let atom = parse_atom(trim_suffix(rest, '.')?)?;
if !atom.is_ground() {
@ -367,6 +375,18 @@ mod tests {
}
}
#[test]
fn parse_sql_command() {
let command = parse_command("sql SELECT c0 FROM Parent WHERE c1 = 'bob';").unwrap();
match command {
Command::Sql(select) => {
assert_eq!(select.from, "Parent");
assert!(select.selection.is_some());
}
other => panic!("unexpected command: {:?}", other),
}
}
#[test]
fn parse_query_command() {
let command = parse_command("query Ancestor(?X, ?Y), Parent(?Y, ?Z)?").unwrap();

80
src/frontend/session.rs
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@ -2,9 +2,13 @@
use std::fmt;
use crate::catalog::PredicateCatalog;
use crate::chase::{
Atom, Instance, MaterializedState, Rule, Substitution, find_matches, materialize,
};
use crate::execution::execute;
use crate::planner::sql::plan_select;
use crate::relational::ResultSet;
use super::language::{Command, parse_script};
use super::provenance::explain_atom;
@ -59,6 +63,7 @@ impl Session {
self.rules.push(rule.clone());
Ok(format!("Added rule #{}: {}", self.rules.len(), rule))
}
Command::Sql(select) => self.run_sql(&select),
Command::Run => Ok(self.run_chase()),
Command::Query(query) => Ok(self.run_query(&query)),
Command::Explain(query) => Ok(self.explain_query(&query)),
@ -123,6 +128,14 @@ impl Session {
rendered.join("\n")
}
fn run_sql(&self, select: &crate::sql::ast::Select) -> Result<String, String> {
let instance = self.active_instance();
let catalog = PredicateCatalog::from_instance(instance).map_err(|err| err.to_string())?;
let plan = plan_select(select, &catalog).map_err(|err| err.to_string())?;
let result = execute(&plan, instance).map_err(|err| err.to_string())?;
Ok(render_result_set(&result))
}
fn explain_query(&self, query: &[Atom]) -> String {
let instance = self.active_instance();
let matches = find_matches(instance, query);
@ -198,6 +211,7 @@ fn help_text() -> &'static str {
"Commands:
fact Parent(alice, bob).
rule Parent(?X, ?Y) -> Ancestor(?X, ?Y).
sql SELECT * FROM Parent;
run.
query Ancestor(?X, ?Y)?
explain Ancestor(alice, bob)?
@ -216,6 +230,39 @@ where
rendered
}
fn render_result_set(result: &ResultSet) -> String {
let mut lines = Vec::new();
lines.push(format!("{} row(s)", result.rows().len()));
if result.schema().is_empty() {
return lines.join("\n");
}
let header = result
.schema()
.fields()
.iter()
.map(|field| field.name().to_string())
.collect::<Vec<_>>()
.join(" | ");
lines.push(header);
let mut rows = result
.rows()
.iter()
.map(|row| {
row.values()
.iter()
.map(ToString::to_string)
.collect::<Vec<_>>()
.join(" | ")
})
.collect::<Vec<_>>();
rows.sort();
lines.extend(rows);
lines.join("\n")
}
fn query_variables(query: &[Atom]) -> Vec<String> {
let mut variables = query
.iter()
@ -286,4 +333,37 @@ mod tests {
assert!(output.contains("premise: Ancestor(alice, bob)"));
assert!(output.contains("input fact"));
}
#[test]
fn session_runs_sql_query() {
let mut session = Session::new();
let output = session
.execute_script(
"fact Parent(alice, bob).\n\
fact Parent(bob, carol).\n\
sql SELECT c0 FROM Parent WHERE c1 = 'bob';",
)
.unwrap();
assert!(output.contains("1 row(s)"));
assert!(output.contains("c0"));
assert!(output.contains("alice"));
}
#[test]
fn session_runs_sql_query_with_alias_and_literal_projection() {
let mut session = Session::new();
let output = session
.execute_script(
"fact Parent(alice, bob).\n\
fact Parent(bob, carol).\n\
sql SELECT c0 AS parent_name, 'seed' AS label FROM Parent;",
)
.unwrap();
assert!(output.contains("2 row(s)"));
assert!(output.contains("parent_name | label"));
assert!(output.contains("alice | seed"));
assert!(output.contains("bob | seed"));
}
}

25
src/planner/logical.rs
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@ -1,28 +1,36 @@
use crate::relational::{ResultSet, Schema, Value};
use crate::relational::{Schema, Value};
/// A logical expression over relational data.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum LogicalExpr {
/// A column reference.
Column(String),
/// A literal value.
Literal(Value),
/// Equality.
Eq(Box<LogicalExpr>, Box<LogicalExpr>),
}
/// A named output expression in a projection.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct NamedExpr {
/// Output column name.
pub name: String,
/// Expression to evaluate.
pub expr: LogicalExpr,
}
/// A logical plan in the current execution subset.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum LogicalPlan {
Scan {
table: String,
schema: Schema,
},
/// Read all facts for one predicate-backed table.
Scan { table: String, schema: Schema },
/// Filter rows by a predicate.
Filter {
input: Box<LogicalPlan>,
predicate: LogicalExpr,
},
/// Project a new output schema.
Project {
input: Box<LogicalPlan>,
expressions: Vec<NamedExpr>,
@ -31,6 +39,7 @@ pub enum LogicalPlan {
}
impl LogicalPlan {
/// Return the schema produced by this logical plan.
pub fn output_schema(&self) -> &Schema {
match self {
Self::Scan { schema, .. } => schema,
@ -39,9 +48,3 @@ impl LogicalPlan {
}
}
}
impl From<ResultSet> for LogicalPlan {
fn from(_: ResultSet) -> Self {
unreachable!("result sets are execution output, not logical plans")
}
}

8
src/planner/mod.rs
View File

@ -1,4 +1,12 @@
//! Logical planning scaffolding.
//!
//! The planner is split into:
//!
//! - [`logical`]: plan and expression data structures
//! - [`sql`]: translation from SQL AST into the current logical-plan subset
//!
//! At the moment this is intentionally small and only covers the first
//! single-table SQL slice.
pub mod logical;
pub mod sql;

90
src/planner/sql.rs
View File

@ -3,14 +3,16 @@ use std::fmt;
use crate::catalog::{CatalogError, PredicateCatalog};
use crate::planner::logical::{LogicalExpr, LogicalPlan, NamedExpr};
use crate::relational::{Field, Schema, Value};
use crate::relational::{DataType, Field, Schema, Value};
use crate::sql::ast::{BinaryOp, Expr, Literal, Select, SelectItem};
/// Errors returned when translating SQL AST into a logical plan.
#[derive(Debug)]
pub enum PlannerError {
/// Catalog lookup failed.
Catalog(CatalogError),
/// A referenced column does not exist in the input schema.
UnknownColumn(String),
UnsupportedProjection,
}
impl fmt::Display for PlannerError {
@ -18,9 +20,6 @@ impl fmt::Display for PlannerError {
match self {
Self::Catalog(err) => write!(f, "catalog error: {}", err),
Self::UnknownColumn(column) => write!(f, "unknown column `{}`", column),
Self::UnsupportedProjection => {
write!(f, "only wildcard and column projections are supported")
}
}
}
}
@ -29,7 +28,7 @@ impl Error for PlannerError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
match self {
Self::Catalog(err) => Some(err),
Self::UnknownColumn(_) | Self::UnsupportedProjection => None,
Self::UnknownColumn(_) => None,
}
}
}
@ -40,6 +39,7 @@ impl From<CatalogError> for PlannerError {
}
}
/// Plan a parsed `SELECT` statement into the current logical plan subset.
pub fn plan_select(
select: &Select,
catalog: &PredicateCatalog,
@ -64,28 +64,21 @@ pub fn plan_select(
let mut expressions = Vec::new();
let mut fields = Vec::new();
for item in &select.projection {
for (index, item) in select.projection.iter().enumerate() {
match item {
SelectItem::Expr { expr, alias } => match expr {
Expr::Identifier(name) => {
let index = scan_schema
.index_of(name)
.ok_or_else(|| PlannerError::UnknownColumn(name.clone()))?;
let input_field = &scan_schema.fields()[index];
let output_name = alias.clone().unwrap_or_else(|| name.clone());
expressions.push(NamedExpr {
name: output_name.clone(),
expr: LogicalExpr::Column(name.clone()),
});
fields.push(Field::new(
output_name,
input_field.data_type().clone(),
input_field.nullable(),
));
}
_ => return Err(PlannerError::UnsupportedProjection),
},
SelectItem::Wildcard => return Err(PlannerError::UnsupportedProjection),
SelectItem::Expr { expr, alias } => {
let planned_expr = plan_expr(expr, &scan_schema)?;
let output_name = alias
.clone()
.unwrap_or_else(|| default_projection_name(expr, index + 1));
let (data_type, nullable) = projection_metadata(expr, &scan_schema)?;
expressions.push(NamedExpr {
name: output_name.clone(),
expr: planned_expr,
});
fields.push(Field::new(output_name, data_type, nullable));
}
SelectItem::Wildcard => unreachable!("wildcard projections are handled earlier"),
}
}
@ -125,6 +118,28 @@ fn plan_literal(literal: &Literal) -> Value {
}
}
fn projection_metadata(expr: &Expr, schema: &Schema) -> Result<(DataType, bool), PlannerError> {
match expr {
Expr::Identifier(name) => {
let index = schema
.index_of(name)
.ok_or_else(|| PlannerError::UnknownColumn(name.clone()))?;
let field = &schema.fields()[index];
Ok((field.data_type().clone(), field.nullable()))
}
Expr::Literal(Literal::String(_)) => Ok((DataType::Text, false)),
Expr::Literal(Literal::Null) => Ok((DataType::Text, true)),
Expr::Binary { .. } => Ok((DataType::Boolean, true)),
}
}
fn default_projection_name(expr: &Expr, ordinal: usize) -> String {
match expr {
Expr::Identifier(name) => name.clone(),
Expr::Literal(_) | Expr::Binary { .. } => format!("expr{}", ordinal),
}
}
#[cfg(test)]
mod tests {
use super::*;
@ -146,4 +161,25 @@ mod tests {
let plan = plan_select(&select, &catalog).unwrap();
assert_eq!(plan.output_schema().len(), 1);
}
#[test]
fn plans_aliases_and_literal_projection() {
let instance: Instance = vec![Atom::new(
"Parent",
vec![Term::constant("alice"), Term::constant("bob")],
)]
.into_iter()
.collect();
let catalog = PredicateCatalog::from_instance(&instance).unwrap();
let select =
parse_select("SELECT c0 AS parent_name, 'seed' AS label, NULL FROM Parent").unwrap();
let plan = plan_select(&select, &catalog).unwrap();
let schema = plan.output_schema();
assert_eq!(schema.len(), 3);
assert_eq!(schema.fields()[0].name(), "parent_name");
assert_eq!(schema.fields()[1].name(), "label");
assert_eq!(schema.fields()[2].name(), "expr3");
assert_eq!(schema.fields()[1].data_type(), &DataType::Text);
}
}

8
src/relational/mod.rs
View File

@ -1,4 +1,10 @@
//! Relational data model scaffolding for future SQL and planner work.
//! Relational data model scaffolding for SQL and planner work.
//!
//! This module provides the current relational execution vocabulary:
//!
//! - [`Schema`] and [`Field`] for column metadata
//! - [`Value`] for scalar values
//! - [`Row`] and [`ResultSet`] for execution output
mod row;
mod schema;

8
src/relational/row.rs
View File

@ -1,24 +1,29 @@
use super::{Schema, Value};
/// One row of relational output values.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Row {
values: Vec<Value>,
}
impl Row {
/// Create a row from ordered values.
pub fn new(values: Vec<Value>) -> Self {
Self { values }
}
/// Return all values in order.
pub fn values(&self) -> &[Value] {
&self.values
}
/// Return the value at a column index.
pub fn get(&self, index: usize) -> Option<&Value> {
self.values.get(index)
}
}
/// A relational query result with a schema and ordered rows.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ResultSet {
schema: Schema,
@ -26,14 +31,17 @@ pub struct ResultSet {
}
impl ResultSet {
/// Create a result set from a schema and rows.
pub fn new(schema: Schema, rows: Vec<Row>) -> Self {
Self { schema, rows }
}
/// Return the output schema.
pub fn schema(&self) -> &Schema {
&self.schema
}
/// Return all output rows.
pub fn rows(&self) -> &[Row] {
&self.rows
}

14
src/relational/schema.rs
View File

@ -1,11 +1,15 @@
use std::fmt;
/// A scalar type supported by the current relational layer.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum DataType {
/// UTF-8 text values.
Text,
/// Boolean values.
Boolean,
}
/// Metadata for one output column in a schema.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Field {
name: String,
@ -14,6 +18,7 @@ pub struct Field {
}
impl Field {
/// Create a field definition.
pub fn new(name: impl Into<String>, data_type: DataType, nullable: bool) -> Self {
Self {
name: name.into(),
@ -22,41 +27,50 @@ impl Field {
}
}
/// Return the field name.
pub fn name(&self) -> &str {
&self.name
}
/// Return the field data type.
pub fn data_type(&self) -> &DataType {
&self.data_type
}
/// Return whether the field may contain null values.
pub fn nullable(&self) -> bool {
self.nullable
}
}
/// An ordered set of named output fields.
#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub struct Schema {
fields: Vec<Field>,
}
impl Schema {
/// Create a schema from a list of fields.
pub fn new(fields: Vec<Field>) -> Self {
Self { fields }
}
/// Return all fields in order.
pub fn fields(&self) -> &[Field] {
&self.fields
}
/// Return the number of fields.
pub fn len(&self) -> usize {
self.fields.len()
}
/// Return whether the schema has no fields.
pub fn is_empty(&self) -> bool {
self.fields.is_empty()
}
/// Look up a field index by column name.
pub fn index_of(&self, name: &str) -> Option<usize> {
self.fields.iter().position(|field| field.name() == name)
}

9
src/relational/value.rs
View File

@ -1,21 +1,30 @@
use std::fmt;
/// A scalar value in the current relational execution layer.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum Value {
/// Textual data.
Text(String),
/// Boolean data.
Boolean(bool),
/// SQL-style null.
Null,
}
impl Value {
/// Create a text value.
pub fn text(value: impl Into<String>) -> Self {
Self::Text(value.into())
}
/// Return whether this value is null.
pub fn is_null(&self) -> bool {
matches!(self, Self::Null)
}
/// Evaluate SQL equality semantics for two scalar values.
///
/// Returns `None` when either side is `NULL`.
pub fn sql_eq(&self, other: &Self) -> Option<bool> {
match (self, other) {
(Self::Null, _) | (_, Self::Null) => None,

16
src/sql/ast.rs
View File

@ -1,20 +1,31 @@
/// A parsed `SELECT-FROM-WHERE` statement in the current SQL subset.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Select {
/// Output expressions requested by the query.
pub projection: Vec<SelectItem>,
/// Source table name.
pub from: String,
/// Optional filter predicate.
pub selection: Option<Expr>,
}
/// One item in a `SELECT` projection list.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum SelectItem {
/// `*`
Wildcard,
/// A projected expression, optionally renamed with `AS`.
Expr { expr: Expr, alias: Option<String> },
}
/// A SQL expression in the current subset.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Expr {
/// A column reference.
Identifier(String),
/// A literal value.
Literal(Literal),
/// A binary expression.
Binary {
left: Box<Expr>,
op: BinaryOp,
@ -22,13 +33,18 @@ pub enum Expr {
},
}
/// A SQL literal in the current subset.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Literal {
/// A string literal.
String(String),
/// The `NULL` literal.
Null,
}
/// A binary operator in the current subset.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum BinaryOp {
/// Equality.
Eq,
}

8
src/sql/mod.rs
View File

@ -1,4 +1,12 @@
//! Minimal SQL front-end scaffolding.
//!
//! The current SQL layer supports a narrow `SELECT-FROM-WHERE` subset over one
//! predicate-backed table. It provides:
//!
//! - a small AST in [`ast`]
//! - a parser in [`parser`]
//!
//! The resulting AST is translated into logical plans by `crate::planner::sql`.
pub mod ast;
pub mod parser;

56
src/sql/parser.rs
View File

@ -3,6 +3,7 @@ use std::fmt;
use super::ast::{BinaryOp, Expr, Literal, Select, SelectItem};
/// Errors returned by the minimal SQL parser.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ParseError {
UnexpectedEnd,
@ -31,6 +32,7 @@ enum Token {
Select,
From,
Where,
As,
Null,
Identifier(String),
String(String),
@ -39,6 +41,7 @@ enum Token {
Eq,
}
/// Parse a `SELECT-FROM-WHERE` query in the current SQL subset.
pub fn parse_select(input: &str) -> Result<Select, ParseError> {
let tokens = tokenize(input)?;
let mut parser = Parser::new(tokens);
@ -82,13 +85,21 @@ impl Parser {
let mut items = Vec::new();
loop {
let item = match self.next().ok_or(ParseError::UnexpectedEnd)? {
Token::Star => SelectItem::Wildcard,
Token::Identifier(name) => SelectItem::Expr {
expr: Expr::Identifier(name),
alias: None,
},
other => return Err(ParseError::UnexpectedToken(render_token(&other))),
let item = match self.peek().ok_or(ParseError::UnexpectedEnd)? {
Token::Star => {
self.index += 1;
SelectItem::Wildcard
}
_ => {
let expr = self.parse_operand()?;
let alias = if self.peek() == Some(&Token::As) {
self.index += 1;
Some(self.expect_identifier()?)
} else {
None
};
SelectItem::Expr { expr, alias }
}
};
items.push(item);
@ -185,6 +196,7 @@ fn tokenize(input: &str) -> Result<Vec<Token>, ParseError> {
"SELECT" => Token::Select,
"FROM" => Token::From,
"WHERE" => Token::Where,
"AS" => Token::As,
"NULL" => Token::Null,
_ => Token::Identifier(ident),
};
@ -251,6 +263,7 @@ fn render_token(token: &Token) -> String {
Token::Select => "SELECT".to_string(),
Token::From => "FROM".to_string(),
Token::Where => "WHERE".to_string(),
Token::As => "AS".to_string(),
Token::Null => "NULL".to_string(),
Token::Identifier(name) => name.clone(),
Token::String(value) => format!("'{}'", value),
@ -272,4 +285,33 @@ mod tests {
assert_eq!(select.projection.len(), 1);
assert!(select.selection.is_some());
}
#[test]
fn parses_projection_aliases_and_literals() {
let select =
parse_select("SELECT c0 AS parent_name, 'seed' AS label, NULL FROM Parent").unwrap();
assert_eq!(select.projection.len(), 3);
assert_eq!(
select.projection[0],
SelectItem::Expr {
expr: Expr::Identifier("c0".to_string()),
alias: Some("parent_name".to_string()),
}
);
assert_eq!(
select.projection[1],
SelectItem::Expr {
expr: Expr::Literal(Literal::String("seed".to_string())),
alias: Some("label".to_string()),
}
);
assert_eq!(
select.projection[2],
SelectItem::Expr {
expr: Expr::Literal(Literal::Null),
alias: None,
}
);
}
}

18
tests/sql_pipeline_tests.rs
View File

@ -65,3 +65,21 @@ fn select_where_filters_rows() {
assert_eq!(result.rows().len(), 1);
assert_eq!(format!("{}", result.rows()[0].values()[0]), "alice");
}
#[test]
fn select_alias_and_literal_projection_shape_output() {
let instance = parent_instance();
let catalog = PredicateCatalog::from_instance(&instance).unwrap();
let select =
parse_select("SELECT c0 AS parent_name, 'seed' AS label, NULL FROM Parent").unwrap();
let plan = plan_select(&select, &catalog).unwrap();
let result = execute(&plan, &instance).unwrap();
assert_eq!(result.schema().fields()[0].name(), "parent_name");
assert_eq!(result.schema().fields()[1].name(), "label");
assert_eq!(result.schema().fields()[2].name(), "expr3");
assert_eq!(result.rows().len(), 2);
assert_eq!(format!("{}", result.rows()[0].values()[1]), "seed");
assert_eq!(format!("{}", result.rows()[0].values()[2]), "NULL");
}