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feat: Allow repeated aliases (auto-realias) #187

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Merged
merged 1 commit into from
Aug 8, 2025
Merged

feat: Allow repeated aliases (auto-realias) #187

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12 changes: 11 additions & 1 deletion datafusion/core/src/logical_plan/builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,10 @@ use crate::logical_plan::{
CrossJoin, DFField, DFSchema, DFSchemaRef, Limit, Partitioning, Repartition,
SubqueryType, Values,
};
use crate::sql::utils::{group_window_expr_by_sort_keys, resolve_exprs_to_aliases};
use crate::sql::utils::{
group_window_expr_by_sort_keys, realias_duplicate_expr_aliases,
resolve_exprs_to_aliases,
};

/// Default table name for unnamed table
pub const UNNAMED_TABLE: &str = "?table?";
Expand Down Expand Up @@ -1222,6 +1225,13 @@ pub fn project_with_alias(
.push(columnize_expr(normalize_col(e, &plan)?, input_schema)),
}
}

// NOTE (cubesql): realias expressions that have the same name and qualifier
if alias.is_some() {
projected_expr =
realias_duplicate_expr_aliases(projected_expr, input_schema, alias.clone())?;
}

validate_unique_names("Projections", projected_expr.iter(), input_schema)?;
let input_schema = DFSchema::new_with_metadata(
exprlist_to_fields(&projected_expr, &plan)?,
Expand Down
116 changes: 84 additions & 32 deletions datafusion/core/src/sql/planner.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,9 @@ use crate::logical_plan::{
use crate::optimizer::utils::exprlist_to_columns;
use crate::prelude::JoinType;
use crate::scalar::ScalarValue;
use crate::sql::utils::{find_udtf_exprs, make_decimal_type, normalize_ident};
use crate::sql::utils::{
find_udtf_exprs, make_decimal_type, normalize_ident, realias_duplicate_expr_aliases,
};
use crate::{
error::{DataFusionError, Result},
physical_plan::aggregates,
Expand Down Expand Up @@ -1038,6 +1040,10 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
);
}

// NOTE (cubesql): realias expressions that have the same name and qualifier
let select_exprs =
realias_duplicate_expr_aliases(select_exprs, plan.schema(), None)?;

// having and group by clause may reference aliases defined in select projection
let projected_plan = self.project(plan.clone(), select_exprs.clone())?;

Expand Down Expand Up @@ -3191,21 +3197,35 @@ mod tests {

#[test]
fn select_repeated_column() {
let sql = "SELECT age, age FROM person";
let err = logical_plan(sql).expect_err("query should have failed");
assert_eq!(
r##"Plan("Projections require unique expression names but the expression \"#person.age\" at position 0 and \"#person.age\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
format!("{:?}", err)
// let sql = "SELECT age, age FROM person";
// let err = logical_plan(sql).expect_err("query should have failed");
// assert_eq!(
// r##"Plan("Projections require unique expression names but the expression \"#person.age\" at position 0 and \"#person.age\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
// format!("{:?}", err)
// );

// NOTE: this is supported with cubesql patches
quick_test(
"SELECT age, age FROM person",
"Projection: #person.age, #person.age AS age__1\
\n TableScan: person projection=None",
);
}

#[test]
fn select_wildcard_with_repeated_column() {
let sql = "SELECT *, age FROM person";
let err = logical_plan(sql).expect_err("query should have failed");
assert_eq!(
r##"Plan("Projections require unique expression names but the expression \"#person.age\" at position 3 and \"#person.age\" at position 8 have the same name. Consider aliasing (\"AS\") one of them.")"##,
format!("{:?}", err)
// let sql = "SELECT *, age FROM person";
// let err = logical_plan(sql).expect_err("query should have failed");
// assert_eq!(
// r##"Plan("Projections require unique expression names but the expression \"#person.age\" at position 3 and \"#person.age\" at position 8 have the same name. Consider aliasing (\"AS\") one of them.")"##,
// format!("{:?}", err)
// );

// NOTE: this is supported with cubesql patches
quick_test(
"SELECT *, age FROM person",
"Projection: #person.id, #person.first_name, #person.last_name, #person.age, #person.state, #person.salary, #person.birth_date, #person.😀, #person.age AS age__1\
\n TableScan: person projection=None",
);
}

Expand Down Expand Up @@ -3779,11 +3799,19 @@ mod tests {

#[test]
fn select_simple_aggregate_repeated_aggregate() {
let sql = "SELECT MIN(age), MIN(age) FROM person";
let err = logical_plan(sql).expect_err("query should have failed");
assert_eq!(
r##"Plan("Projections require unique expression names but the expression \"MIN(#person.age)\" at position 0 and \"MIN(#person.age)\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
format!("{:?}", err)
// let sql = "SELECT MIN(age), MIN(age) FROM person";
// let err = logical_plan(sql).expect_err("query should have failed");
// assert_eq!(
// r##"Plan("Projections require unique expression names but the expression \"MIN(#person.age)\" at position 0 and \"MIN(#person.age)\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
// format!("{:?}", err)
// );

// NOTE: this is supported with cubesql patches
quick_test(
"SELECT MIN(age), MIN(age) FROM person",
"Projection: #MIN(person.age), #MIN(person.age) AS MIN(person.age)__1\
\n Aggregate: groupBy=[[]], aggr=[[MIN(#person.age)]]\
\n TableScan: person projection=None",
);
}

Expand All @@ -3809,11 +3837,19 @@ mod tests {

#[test]
fn select_simple_aggregate_repeated_aggregate_with_repeated_aliases() {
let sql = "SELECT MIN(age) AS a, MIN(age) AS a FROM person";
let err = logical_plan(sql).expect_err("query should have failed");
assert_eq!(
r##"Plan("Projections require unique expression names but the expression \"MIN(#person.age) AS a\" at position 0 and \"MIN(#person.age) AS a\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
format!("{:?}", err)
// let sql = "SELECT MIN(age) AS a, MIN(age) AS a FROM person";
// let err = logical_plan(sql).expect_err("query should have failed");
// assert_eq!(
// r##"Plan("Projections require unique expression names but the expression \"MIN(#person.age) AS a\" at position 0 and \"MIN(#person.age) AS a\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
// format!("{:?}", err)
// );

// NOTE: this is supported with cubesql patches
quick_test(
"SELECT MIN(age) AS a, MIN(age) AS a FROM person",
"Projection: #MIN(person.age) AS a, #MIN(person.age) AS a__1\
\n Aggregate: groupBy=[[]], aggr=[[MIN(#person.age)]]\
\n TableScan: person projection=None",
);
}

Expand All @@ -3839,11 +3875,19 @@ mod tests {

#[test]
fn select_simple_aggregate_with_groupby_with_aliases_repeated() {
let sql = "SELECT state AS a, MIN(age) AS a FROM person GROUP BY state";
let err = logical_plan(sql).expect_err("query should have failed");
assert_eq!(
r##"Plan("Projections require unique expression names but the expression \"#person.state AS a\" at position 0 and \"MIN(#person.age) AS a\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
format!("{:?}", err)
// let sql = "SELECT state AS a, MIN(age) AS a FROM person GROUP BY state";
// let err = logical_plan(sql).expect_err("query should have failed");
// assert_eq!(
// r##"Plan("Projections require unique expression names but the expression \"#person.state AS a\" at position 0 and \"MIN(#person.age) AS a\" at position 1 have the same name. Consider aliasing (\"AS\") one of them.")"##,
// format!("{:?}", err)
// );

// NOTE: this is supported with cubesql patches
quick_test(
"SELECT state AS a, MIN(age) AS a FROM person GROUP BY state",
"Projection: #person.state AS a, #MIN(person.age) AS a__1\
\n Aggregate: groupBy=[[#person.state]], aggr=[[MIN(#person.age)]]\
\n TableScan: person projection=None",
);
}

Expand Down Expand Up @@ -4008,12 +4052,20 @@ mod tests {

#[test]
fn select_simple_aggregate_with_groupby_aggregate_repeated() {
let sql = "SELECT state, MIN(age), MIN(age) FROM person GROUP BY state";
let err = logical_plan(sql).expect_err("query should have failed");
assert_eq!(
r##"Plan("Projections require unique expression names but the expression \"MIN(#person.age)\" at position 1 and \"MIN(#person.age)\" at position 2 have the same name. Consider aliasing (\"AS\") one of them.")"##,
format!("{:?}", err)
);
// let sql = "SELECT state, MIN(age), MIN(age) FROM person GROUP BY state";
// let err = logical_plan(sql).expect_err("query should have failed");
// assert_eq!(
// r##"Plan("Projections require unique expression names but the expression \"MIN(#person.age)\" at position 1 and \"MIN(#person.age)\" at position 2 have the same name. Consider aliasing (\"AS\") one of them.")"##,
// format!("{:?}", err)
// );

// NOTE: this is supported with cubesql patches
quick_test(
"SELECT state, MIN(age), MIN(age) FROM person GROUP BY state",
"Projection: #person.state, #MIN(person.age), #MIN(person.age) AS MIN(person.age)__1\
\n Aggregate: groupBy=[[#person.state]], aggr=[[MIN(#person.age)]]\
\n TableScan: person projection=None",
)
}

#[test]
Expand Down
93 changes: 91 additions & 2 deletions datafusion/core/src/sql/utils.rs
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Expand Up @@ -21,15 +21,16 @@ use arrow::datatypes::{DataType, DECIMAL_DEFAULT_SCALE, DECIMAL_MAX_PRECISION};
use datafusion_common::DFSchema;
use sqlparser::ast::Ident;

use crate::logical_plan::ExprVisitable;
use crate::logical_plan::{Expr, Like, LogicalPlan};
use crate::logical_plan::{ExprSchemable, ExprVisitable};
use crate::scalar::ScalarValue;
use crate::{
error::{DataFusionError, Result},
logical_plan::{Column, ExpressionVisitor, Recursion},
};
use datafusion_expr::expr::GroupingSet;
use std::collections::HashMap;
use std::collections::{HashMap, HashSet};
use std::mem::replace;

/// Collect all deeply nested `Expr::AggregateFunction` and
/// `Expr::AggregateUDF`. They are returned in order of occurrence (depth
Expand Down Expand Up @@ -781,6 +782,94 @@ pub(crate) fn normalize_ident(id: Ident) -> String {
id.value
}

/// Structure holding qualifier and name of an alias.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct QualifiedAlias {
qualifier: Option<String>,
name: String,
}

impl QualifiedAlias {
fn new(qualifier: Option<String>, name: String) -> Self {
Self { qualifier, name }
}

fn from_expr_schema_and_alias(
expr: &Expr,
schema: &DFSchema,
alias: Option<String>,
) -> Result<Self> {
let field = expr.to_field(schema)?;
let qualifier = alias.or_else(|| field.qualifier().cloned());
let name = field.name().clone();
Ok(Self::new(qualifier, name))
}

fn with_name(&self, name: &str) -> Self {
Self {
qualifier: self.qualifier.clone(),
name: name.to_string(),
}
}
}

/// Realias duplicate expression aliases in the provided list of expressions.
pub(crate) fn realias_duplicate_expr_aliases(
mut exprs: Vec<Expr>,
schema: &DFSchema,
alias: Option<String>,
) -> Result<Vec<Expr>> {
// Two-pass algorithm is used: first collect all the aliases and indices of repeated aliases,
// then realias the collected indices on the second pass.
// This is to avoid realiasing to a name that is valid but is used by another expression
// that was not originally processed.
let mut aliases = HashSet::new();
let mut indices_to_realias = vec![];
for (index, expr) in exprs.iter().enumerate() {
let qualified_alias =
QualifiedAlias::from_expr_schema_and_alias(expr, schema, alias.clone())?;
let is_duplicate = !aliases.insert(qualified_alias);
if is_duplicate {
indices_to_realias.push(index);
}
}
const MAX_SUFFIX_LIMIT: usize = 100;
'outer: for index in indices_to_realias {
let qualified_alias = QualifiedAlias::from_expr_schema_and_alias(
&exprs[index],
schema,
alias.clone(),
)?;
for suffix in 1..=MAX_SUFFIX_LIMIT {
let new_name = format!("{}__{}", qualified_alias.name, suffix);
let new_qualified_alias = qualified_alias.with_name(&new_name);
let is_duplicate = !aliases.insert(new_qualified_alias);
if !is_duplicate {
set_expr_alias(&mut exprs[index], new_name);
continue 'outer;
}
}
return Err(DataFusionError::Internal(format!(
"Unable to realias duplicate expression alias: {:?}",
exprs[index]
)));
}
Ok(exprs)
}

/// Set an alias for an expression, replacing an existing alias or adding one if necessary.
fn set_expr_alias(expr: &mut Expr, alias: String) {
match expr {
Expr::Alias(_, name) => {
*name = alias;
}
_ => {
// Expr::Wildcard is simply a placeholder to please borrow checker
*expr = Expr::Alias(Box::new(replace(expr, Expr::Wildcard)), alias);
Comment on lines +867 to +868
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Copilot AI Aug 6, 2025

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The comment suggests this is a workaround for the borrow checker, but it's unclear why Expr::Wildcard was chosen as the placeholder. Consider explaining why this specific variant is appropriate or if there's a better alternative.

Suggested change
// Expr::Wildcard is simply a placeholder to please borrow checker
*expr = Expr::Alias(Box::new(replace(expr, Expr::Wildcard)), alias);
// Use std::mem::replace to move the original expression into the Alias variant.
// This avoids borrow checker issues and preserves the original expression semantics.
*expr = Expr::Alias(Box::new(replace(expr, Expr::Alias(Box::new(Expr::Literal(ScalarValue::Null)), alias.clone()))), alias);

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}
}
}

#[cfg(test)]
mod tests {
use super::*;
Expand Down
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