sheeter_engine/

query.rs

//! SQL query engine over files.
//!
//! [`run`] parses a `SELECT` statement, resolves file paths from the `FROM`
//! clause relative to a base directory, executes the query in memory, and
//! returns the result as a [`CanonicalValue::Array`] of row objects. The
//! supported surface is deliberately small: `SELECT` with column references,
//! aliases, and arithmetic; `WHERE`; `GROUP BY` with `SUM`, `AVG`, `COUNT`,
//! `MIN`, and `MAX`; `HAVING` (evaluated on projected aliases); `ORDER BY`;
//! `LIMIT`; `DISTINCT`; `INNER JOIN` and `LEFT JOIN` with `ON`; and a
//! `FROM` clause that accepts a single file, a quoted glob pattern, or a
//! comma-separated list of tables (which produces a cross join).
//!
//! Every format the sheeter engine reads can appear in `FROM`, so a single
//! query can mix `.xlsx`, `.csv`, `.json`, `.ndjson`, `.yaml`, `.xml`,
//! `.toml`, `.ods`, and `.sql` files without conversion.
//!
//! # Examples
//!
//! ```
//! use sheeter_engine::query;
//! use std::fs;
//!
//! let dir = tempfile::tempdir().unwrap();
//! fs::write(dir.path().join("users.csv"), "id,name\n1,Alice\n2,Bob\n").unwrap();
//! let result = query::run("SELECT name FROM users.csv WHERE id = 2", dir.path()).unwrap();
//! assert_eq!(result.to_json().unwrap(), r#"[{"name":"Bob"}]"#);
//! ```

use crate::{detect_content, detect_extension, CanonicalValue, Format, SqlDialect};
use serde_json::Number;
use sqlparser::ast::{
    BinaryOperator, Expr, FunctionArg, FunctionArgExpr, FunctionArguments, GroupByExpr,
    JoinConstraint, JoinOperator, LimitClause, ObjectNamePart, OrderByExpr, OrderByKind, Query,
    SelectItem, SetExpr, Statement, TableFactor, TableWithJoins, Value, ValueWithSpan,
};
use sqlparser::dialect::GenericDialect;
use sqlparser::parser::Parser;
use std::cmp::Ordering;
use std::collections::{HashMap, HashSet};
use std::error::Error;
use std::path::{Path, PathBuf};

type Row = Vec<(String, CanonicalValue)>;

/// Executes a `SELECT` statement over files in `base_dir`.
///
/// The `FROM` clause is resolved relative to `base_dir`. Each file is
/// decoded using the sheeter engine's format detection, so a single query
/// can join a CSV, an XLSX sheet, and an NDJSON stream without any manual
/// conversion step. The result is returned as a [`CanonicalValue::Array`]
/// whose elements are row objects, ready to be serialized in any format
/// the engine writes.
///
/// Column references may be qualified (`u.name`) or bare (`name`). Bare
/// names are resolved by suffix match, so `name` finds `users.name` when
/// only one table has a column ending in `.name`. Comparison operands are
/// coerced to `f64` when both sides parse as numbers, and to `String`
/// otherwise, so `id = 2` matches a CSV cell that contains the string
/// `"2"`.
///
/// # Errors
///
/// Returns an error if the SQL does not parse, the `FROM` clause references
/// a missing file, a glob pattern fails to expand, a referenced column does
/// not exist in any table, or an arithmetic operation cannot coerce its
/// operands.
///
/// # Examples
///
/// ```
/// use sheeter_engine::query;
/// use std::fs;
///
/// let dir = tempfile::tempdir().unwrap();
/// fs::write(dir.path().join("data.csv"), "a,b\n1,x\n2,y\n3,z\n").unwrap();
/// let result = query::run(
///     "SELECT a FROM data.csv WHERE b != 'z' ORDER BY a DESC",
///     dir.path(),
/// ).unwrap();
/// assert_eq!(result.to_json().unwrap(), r#"[{"a":"2"},{"a":"1"}]"#);
/// ```
pub fn run(sql: &str, base_dir: &Path) -> Result<CanonicalValue, Box<dyn Error>> {
    let stmts = Parser::parse_sql(&GenericDialect {}, sql)?;
    let stmt = stmts.into_iter().next().ok_or("empty SQL")?;
    match stmt {
        Statement::Query(q) => execute_query(*q, base_dir),
        _ => Err("only SELECT statements are supported".into()),
    }
}

fn execute_query(query: Query, base_dir: &Path) -> Result<CanonicalValue, Box<dyn Error>> {
    let body = (*query.body).clone();
    let select = match body {
        SetExpr::Select(s) => *s,
        _ => return Err("only simple SELECT is supported".into()),
    };

    let mut rows = load_from(&select.from, base_dir)?;

    if let Some(pred) = &select.selection {
        let mut kept = Vec::new();
        for row in rows {
            if matches!(eval(pred.clone(), &row), Ok(CanonicalValue::Bool(true))) {
                kept.push(row);
            }
        }
        rows = kept;
    }

    let has_agg = select.projection.iter().any(|item| match item {
        SelectItem::UnnamedExpr(e) | SelectItem::ExprWithAlias { expr: e, .. } => {
            contains_aggregate(e)
        }
        _ => false,
    });
    let group_by = extract_group_by(&select.group_by);

    let mut out_rows = if !group_by.is_empty() || has_agg {
        aggregate(rows, &select.projection, &group_by, &select.having)?
    } else {
        project(rows, &select.projection)?
    };

    if select.distinct.is_some() {
        let mut seen: HashSet<String> = HashSet::new();
        out_rows.retain(|r| {
            let key = r
                .iter()
                .map(|(_, v)| format!("{v:?}"))
                .collect::<Vec<_>>()
                .join("\x1f");
            seen.insert(key)
        });
    }

    if let Some(order) = &query.order_by {
        if let OrderByKind::Expressions(exprs) = &order.kind {
            sort_rows(&mut out_rows, exprs)?;
        }
    }

    if let Some(lc) = &query.limit_clause {
        if let Some(limit_expr) = extract_limit_expr(lc) {
            if let Ok(CanonicalValue::Number(n)) = eval(limit_expr, &Vec::new()) {
                if let Some(limit) = n.as_u64() {
                    out_rows.truncate(limit as usize);
                }
            }
        }
    }

    Ok(CanonicalValue::Array(
        out_rows.into_iter().map(CanonicalValue::Object).collect(),
    ))
}

fn extract_group_by(g: &GroupByExpr) -> Vec<Expr> {
    match g {
        GroupByExpr::Expressions(exprs, _) => exprs.clone(),
        _ => Vec::new(),
    }
}

fn load_from(from: &[TableWithJoins], base_dir: &Path) -> Result<Vec<Row>, Box<dyn Error>> {
    if from.is_empty() {
        return Err("FROM is required".into());
    }
    let mut rows = load_table_with_joins(&from[0], base_dir)?;
    for extra in &from[1..] {
        let more = load_table_with_joins(extra, base_dir)?;
        let mut crossed = Vec::new();
        for a in &rows {
            for b in &more {
                let mut combined = a.clone();
                combined.extend(b.clone());
                crossed.push(combined);
            }
        }
        rows = crossed;
    }
    Ok(rows)
}

fn load_table_with_joins(t: &TableWithJoins, base_dir: &Path) -> Result<Vec<Row>, Box<dyn Error>> {
    let mut rows = load_factor(&t.relation, base_dir)?;
    for join in &t.joins {
        let right = load_factor(&join.relation, base_dir)?;
        rows = apply_join(rows, right, &join.join_operator)?;
    }
    Ok(rows)
}

fn load_factor(factor: &TableFactor, base_dir: &Path) -> Result<Vec<Row>, Box<dyn Error>> {
    let (name, alias) = match factor {
        TableFactor::Table { name, alias, .. } => (name, alias),
        _ => return Err("only table references are supported in FROM".into()),
    };

    let raw = name
        .0
        .iter()
        .filter_map(|p| match p {
            ObjectNamePart::Identifier(i) => Some(i.value.clone()),
            _ => None,
        })
        .collect::<Vec<_>>()
        .join(".");

    let alias_name = alias
        .as_ref()
        .map(|a| a.name.value.clone())
        .unwrap_or_else(|| {
            Path::new(&raw)
                .file_stem()
                .and_then(|s| s.to_str())
                .unwrap_or(&raw)
                .to_string()
        });

    let mut all_rows = Vec::new();
    if is_glob(&raw) {
        let pattern = resolve_path(&raw, base_dir).to_string_lossy().to_string();
        let entries = glob::glob(&pattern).map_err(|e| format!("invalid glob {pattern}: {e}"))?;
        for entry in entries {
            let p = entry?;
            let mut r = load_file(&p)?;
            all_rows.append(&mut r);
        }
    } else {
        all_rows = load_file(&resolve_path(&raw, base_dir))?;
    }

    Ok(all_rows
        .into_iter()
        .map(|row| {
            row.into_iter()
                .map(|(k, v)| (format!("{alias_name}.{k}"), v))
                .collect()
        })
        .collect())
}

fn is_glob(s: &str) -> bool {
    s.contains('*') || s.contains('?') || s.contains('[')
}

fn resolve_path(raw: &str, base_dir: &Path) -> PathBuf {
    let candidate = base_dir.join(raw);
    if candidate.exists() || is_glob(raw) || Path::new(raw).is_absolute() {
        return candidate;
    }
    let parts: Vec<&str> = raw.split('.').collect();
    if parts.len() > 2 {
        let prefix = parts[..parts.len() - 2].join("/");
        let suffix = parts[parts.len() - 2..].join(".");
        let slashed = base_dir.join(format!("{prefix}/{suffix}"));
        if slashed.exists() {
            return slashed;
        }
    }
    candidate
}

fn load_file(path: &Path) -> Result<Vec<Row>, Box<dyn Error>> {
    let bytes = std::fs::read(path)?;
    let fmt = match detect_extension(path) {
        Some(f) => f,
        None => detect_content(&bytes)?,
    };
    let value = decode(fmt, &bytes)?;
    match value {
        CanonicalValue::Array(rows) => Ok(rows
            .into_iter()
            .filter_map(|r| match r {
                CanonicalValue::Object(o) => Some(o),
                _ => None,
            })
            .collect()),
        _ => Err(format!("{} did not produce a table", path.display()).into()),
    }
}

fn decode(fmt: Format, bytes: &[u8]) -> Result<CanonicalValue, Box<dyn Error>> {
    let text = || -> Result<&str, Box<dyn Error>> { Ok(std::str::from_utf8(bytes)?) };
    match fmt {
        Format::Csv => CanonicalValue::from_csv(text()?),
        Format::Tsv => CanonicalValue::from_tsv(text()?),
        Format::Json => CanonicalValue::from_json(text()?),
        Format::Ndjson => CanonicalValue::from_ndjson(text()?),
        Format::Yaml => CanonicalValue::from_yaml(text()?),
        Format::Xml => CanonicalValue::from_xml(text()?),
        Format::Toml => CanonicalValue::from_toml(text()?),
        Format::Xlsx => {
            let mut sheets = CanonicalValue::from_xlsx_workbook(bytes)?;
            if sheets.len() != 1 {
                return Err("multi-sheet XLSX requires a single sheet".into());
            }
            Ok(sheets.remove(0).1)
        }
        Format::Ods => CanonicalValue::from_ods(bytes),
        Format::Sql => {
            let mut sheets = CanonicalValue::from_sql_workbook(text()?, SqlDialect::Generic)?;
            if sheets.len() != 1 {
                return Err("multi-table SQL requires a single table".into());
            }
            Ok(sheets.remove(0).1)
        }
    }
}

fn apply_join(
    left: Vec<Row>,
    right: Vec<Row>,
    op: &JoinOperator,
) -> Result<Vec<Row>, Box<dyn Error>> {
    let (constraint, is_left) = match op {
        JoinOperator::Inner(c) => (c, false),
        JoinOperator::Join(c) => (c, false),
        JoinOperator::LeftOuter(c) => (c, true),
        other => return Err(format!("unsupported join variant: {other:?}").into()),
    };
    let on = match constraint {
        JoinConstraint::On(e) => e.clone(),
        _ => return Err("only JOIN ... ON is supported".into()),
    };

    let mut result = Vec::new();
    for l in &left {
        let mut matched = false;
        for r in &right {
            let mut combined = l.clone();
            combined.extend(r.clone());
            if matches!(eval(on.clone(), &combined), Ok(CanonicalValue::Bool(true))) {
                result.push(combined);
                matched = true;
            }
        }
        if is_left && !matched {
            result.push(l.clone());
        }
    }
    Ok(result)
}

fn eval(expr: Expr, row: &Row) -> Result<CanonicalValue, Box<dyn Error>> {
    match expr {
        Expr::Identifier(i) => resolve_column(&i.value, row),
        Expr::CompoundIdentifier(parts) => {
            let name = parts
                .iter()
                .map(|p| p.value.clone())
                .collect::<Vec<_>>()
                .join(".");
            resolve_column(&name, row)
        }
        Expr::Value(ValueWithSpan { value, .. }) => Ok(literal(value)),
        Expr::BinaryOp { left, op, right } => {
            let l = eval(*left, row)?;
            let r = eval(*right, row)?;
            binary_op(l, &op, r)
        }
        Expr::Nested(inner) => eval(*inner, row),
        other => Err(format!("unsupported expression: {other:?}").into()),
    }
}

fn resolve_column(name: &str, row: &Row) -> Result<CanonicalValue, Box<dyn Error>> {
    if let Some((_, v)) = row.iter().find(|(k, _)| k == name) {
        return Ok(v.clone());
    }
    let suffix = format!(".{name}");
    if let Some((_, v)) = row.iter().find(|(k, _)| k.ends_with(&suffix)) {
        return Ok(v.clone());
    }
    Err(format!("column {name} not found").into())
}

fn literal(v: Value) -> CanonicalValue {
    match v {
        Value::Number(n, _) => {
            if let Ok(i) = n.parse::<i64>() {
                CanonicalValue::Number(Number::from(i))
            } else if let Ok(f) = n.parse::<f64>() {
                Number::from_f64(f)
                    .map(CanonicalValue::Number)
                    .unwrap_or(CanonicalValue::Null)
            } else {
                CanonicalValue::String(n)
            }
        }
        Value::SingleQuotedString(s) | Value::DoubleQuotedString(s) => CanonicalValue::String(s),
        Value::Boolean(b) => CanonicalValue::Bool(b),
        Value::Null => CanonicalValue::Null,
        _ => CanonicalValue::Null,
    }
}

fn binary_op(
    l: CanonicalValue,
    op: &BinaryOperator,
    r: CanonicalValue,
) -> Result<CanonicalValue, Box<dyn Error>> {
    if matches!(l, CanonicalValue::Null) || matches!(r, CanonicalValue::Null) {
        match op {
            BinaryOperator::Eq
            | BinaryOperator::NotEq
            | BinaryOperator::Lt
            | BinaryOperator::LtEq
            | BinaryOperator::Gt
            | BinaryOperator::GtEq => return Ok(CanonicalValue::Bool(false)),
            _ => {}
        }
    }
    let ord = || compare_values(&l, &r);
    match op {
        BinaryOperator::Eq => return Ok(CanonicalValue::Bool(ord() == Ordering::Equal)),
        BinaryOperator::NotEq => return Ok(CanonicalValue::Bool(ord() != Ordering::Equal)),
        BinaryOperator::Lt => return Ok(CanonicalValue::Bool(ord() == Ordering::Less)),
        BinaryOperator::LtEq => return Ok(CanonicalValue::Bool(ord() != Ordering::Greater)),
        BinaryOperator::Gt => return Ok(CanonicalValue::Bool(ord() == Ordering::Greater)),
        BinaryOperator::GtEq => return Ok(CanonicalValue::Bool(ord() != Ordering::Less)),
        BinaryOperator::And => {
            let a = matches!(l, CanonicalValue::Bool(true));
            let b = matches!(r, CanonicalValue::Bool(true));
            return Ok(CanonicalValue::Bool(a && b));
        }
        BinaryOperator::Or => {
            let a = matches!(l, CanonicalValue::Bool(true));
            let b = matches!(r, CanonicalValue::Bool(true));
            return Ok(CanonicalValue::Bool(a || b));
        }
        _ => {}
    }
    let a = to_f64(&l);
    let b = to_f64(&r);
    let result = match (a, b) {
        (Some(a), Some(b)) => match op {
            BinaryOperator::Plus => Some(a + b),
            BinaryOperator::Minus => Some(a - b),
            BinaryOperator::Multiply => Some(a * b),
            BinaryOperator::Divide => Some(a / b),
            _ => None,
        },
        _ => None,
    };
    match result {
        Some(f) => Ok(num(f)),
        None => Err(format!("cannot apply {op:?} to {l:?} and {r:?}").into()),
    }
}

fn to_f64(v: &CanonicalValue) -> Option<f64> {
    match v {
        CanonicalValue::Number(n) => n.as_f64(),
        CanonicalValue::String(s) => s.parse().ok(),
        CanonicalValue::Bool(b) => Some(if *b { 1.0 } else { 0.0 }),
        _ => None,
    }
}

fn num(f: f64) -> CanonicalValue {
    if f.is_finite() && f.fract() == 0.0 && f.abs() < i64::MAX as f64 {
        CanonicalValue::Number(Number::from(f as i64))
    } else {
        Number::from_f64(f)
            .map(CanonicalValue::Number)
            .unwrap_or(CanonicalValue::Null)
    }
}

fn project(rows: Vec<Row>, projection: &[SelectItem]) -> Result<Vec<Row>, Box<dyn Error>> {
    let mut out = Vec::with_capacity(rows.len());
    for row in rows {
        let mut new_row = Vec::new();
        for item in projection {
            match item {
                SelectItem::UnnamedExpr(expr) => {
                    let name = expr_name(expr);
                    new_row.push((name, eval(expr.clone(), &row)?));
                }
                SelectItem::ExprWithAlias { expr, alias } => {
                    new_row.push((alias.value.clone(), eval(expr.clone(), &row)?));
                }
                SelectItem::Wildcard(_) => {
                    for (k, v) in &row {
                        let name = k.rsplit('.').next().unwrap_or(k).to_string();
                        new_row.push((name, v.clone()));
                    }
                }
                SelectItem::QualifiedWildcard(name, _) => {
                    let prefix = format!("{name}.");
                    for (k, v) in &row {
                        if let Some(short) = k.strip_prefix(&prefix) {
                            new_row.push((short.to_string(), v.clone()));
                        }
                    }
                }
                SelectItem::ExprWithAliases { .. } => {
                    return Err("multi-alias SELECT not supported".into());
                }
            }
        }
        out.push(new_row);
    }
    Ok(out)
}

fn expr_name(expr: &Expr) -> String {
    match expr {
        Expr::Identifier(i) => i.value.clone(),
        Expr::CompoundIdentifier(parts) => {
            parts.last().map(|p| p.value.clone()).unwrap_or_default()
        }
        Expr::Function(f) => {
            let fname = f.name.to_string().to_lowercase();
            let arg = match &f.args {
                FunctionArguments::List(l) => l
                    .args
                    .first()
                    .and_then(|a| match a {
                        FunctionArg::Unnamed(FunctionArgExpr::Expr(e)) => Some(expr_name(e)),
                        _ => None,
                    })
                    .unwrap_or_default(),
                _ => String::new(),
            };
            format!("{fname}({arg})")
        }
        Expr::BinaryOp { left, op, right } => {
            format!("{} {} {}", expr_name(left), op, expr_name(right))
        }
        Expr::Nested(inner) => expr_name(inner),
        _ => "expr".to_string(),
    }
}

fn aggregate(
    rows: Vec<Row>,
    projection: &[SelectItem],
    group_by: &[Expr],
    having: &Option<Expr>,
) -> Result<Vec<Row>, Box<dyn Error>> {
    let mut groups: HashMap<Vec<String>, Vec<Row>> = HashMap::new();
    if group_by.is_empty() {
        groups.insert(Vec::new(), rows);
    } else {
        for row in rows {
            let mut key = Vec::new();
            for g in group_by {
                let v = eval(g.clone(), &row)?;
                key.push(format!("{v:?}"));
            }
            groups.entry(key).or_default().push(row);
        }
    }

    let mut out = Vec::new();
    for group in groups.into_values() {
        let mut new_row = Vec::new();
        for item in projection {
            match item {
                SelectItem::UnnamedExpr(expr) => {
                    let name = expr_name(expr);
                    new_row.push((name, eval_aggregated(expr, &group)?));
                }
                SelectItem::ExprWithAlias { expr, alias } => {
                    new_row.push((alias.value.clone(), eval_aggregated(expr, &group)?));
                }
                _ => return Err("unsupported aggregate SELECT item".into()),
            }
        }
        if let Some(h) = having {
            if !matches!(eval(h.clone(), &new_row), Ok(CanonicalValue::Bool(true))) {
                continue;
            }
        }
        out.push(new_row);
    }
    Ok(out)
}

fn eval_aggregated(expr: &Expr, group: &[Row]) -> Result<CanonicalValue, Box<dyn Error>> {
    if let Expr::Function(f) = expr {
        let name = f.name.to_string().to_uppercase();
        if matches!(name.as_str(), "SUM" | "AVG" | "MIN" | "MAX" | "COUNT") {
            let arg = match &f.args {
                FunctionArguments::List(l) => l.args.first().and_then(|a| match a {
                    FunctionArg::Unnamed(FunctionArgExpr::Expr(e)) => Some(e.clone()),
                    _ => None,
                }),
                _ => None,
            };
            return compute_aggregate(&name, arg, group);
        }
    }
    if let Some(first) = group.first() {
        return eval(expr.clone(), first);
    }
    Ok(CanonicalValue::Null)
}

fn compute_aggregate(
    name: &str,
    arg: Option<Expr>,
    group: &[Row],
) -> Result<CanonicalValue, Box<dyn Error>> {
    let arg = match arg {
        Some(a) => a,
        None => {
            return match name {
                "COUNT" => Ok(CanonicalValue::Number(Number::from(group.len() as i64))),
                _ => Err(format!("{name} requires an argument").into()),
            };
        }
    };

    let mut count = 0usize;
    let mut sum = 0.0f64;
    let mut best: Option<f64> = None;

    for row in group {
        if let Ok(v) = eval(arg.clone(), row) {
            if let CanonicalValue::Null = v {
                continue;
            }
            if let Some(f) = to_f64(&v) {
                sum += f;
                count += 1;
                best = Some(match best {
                    None => f,
                    Some(b) => match name {
                        "MIN" => b.min(f),
                        "MAX" => b.max(f),
                        _ => b,
                    },
                });
            }
        }
    }

    Ok(match name {
        "SUM" => num(sum),
        "AVG" => {
            if count > 0 {
                num(sum / count as f64)
            } else {
                CanonicalValue::Null
            }
        }
        "COUNT" => CanonicalValue::Number(Number::from(count as i64)),
        "MIN" | "MAX" => best.map(num).unwrap_or(CanonicalValue::Null),
        _ => CanonicalValue::Null,
    })
}

fn extract_limit_expr(lc: &LimitClause) -> Option<Expr> {
    match lc {
        LimitClause::LimitOffset { limit, .. } => limit.clone(),
        LimitClause::OffsetCommaLimit { limit, .. } => Some(limit.clone()),
    }
}

fn sort_rows(rows: &mut [Row], order_by: &[OrderByExpr]) -> Result<(), Box<dyn Error>> {
    let keys: Vec<(Expr, bool)> = order_by
        .iter()
        .map(|o| (o.expr.clone(), o.options.asc.unwrap_or(true)))
        .collect();
    rows.sort_by(|a, b| {
        for (expr, asc) in &keys {
            let av = eval(expr.clone(), a).unwrap_or(CanonicalValue::Null);
            let bv = eval(expr.clone(), b).unwrap_or(CanonicalValue::Null);
            let ord = compare_values(&av, &bv);
            let ord = if *asc { ord } else { ord.reverse() };
            if ord != Ordering::Equal {
                return ord;
            }
        }
        Ordering::Equal
    });
    Ok(())
}

fn compare_values(a: &CanonicalValue, b: &CanonicalValue) -> Ordering {
    match (a, b) {
        (CanonicalValue::Null, CanonicalValue::Null) => Ordering::Equal,
        (CanonicalValue::Null, _) => Ordering::Less,
        (_, CanonicalValue::Null) => Ordering::Greater,
        _ => {
            if let (Some(x), Some(y)) = (to_f64(a), to_f64(b)) {
                return x.partial_cmp(&y).unwrap_or(Ordering::Equal);
            }
            scalar_string(a).cmp(&scalar_string(b))
        }
    }
}

fn scalar_string(v: &CanonicalValue) -> String {
    match v {
        CanonicalValue::Null => String::new(),
        CanonicalValue::Bool(b) => b.to_string(),
        CanonicalValue::Number(n) => n.to_string(),
        CanonicalValue::String(s) => s.clone(),
        CanonicalValue::Bytes(b) => b.iter().map(|x| format!("{x:02x}")).collect(),
        _ => String::new(),
    }
}

fn contains_aggregate(expr: &Expr) -> bool {
    match expr {
        Expr::Function(f) => {
            let name = f.name.to_string().to_uppercase();
            matches!(name.as_str(), "SUM" | "AVG" | "MIN" | "MAX" | "COUNT")
        }
        Expr::BinaryOp { left, right, .. } => contains_aggregate(left) || contains_aggregate(right),
        Expr::Nested(inner) => contains_aggregate(inner),
        _ => false,
    }
}