inillucent-sql 0.1.9

//! Row values: `(a, b) = (c, d)`, `(a, b) IN ((1, 2), (3, 4))`, and
//! `(a, b) < (SELECT x, y ...)`.
//!
//! Invariant: **nothing below the binder has a row value in it, and this is
//! the only place that stays true.** A row value is a syntax for comparing
//! several columns at once, and it is the whole of what the engine keeps of
//! one: `BoundExpr` has no tuple, the planner has no tuple, and the register
//! machine compares one value against one value. Every spelling here is
//! rewritten into ordinary scalar comparisons joined by `AND`, `OR` and `NOT`
//! before it leaves, so a row value costs the rest of the engine nothing and
//! can never be the reason a later pass has a case it does not handle.
//!
//! That is also why the three desugarings live beside each other rather than
//! next to the operators that reach them. `=` over two rows and `=` over a row
//! and a one-row query are the same chain of equalities over different
//! operands, and `<` over two rows is the lexicographic chain that `IN` does
//! not need at all - but all three have to agree about NULL, about affinity and
//! about collation, or `(1, NULL) <> (1, 2)` answers differently depending on
//! which spelling was written. They agree because they are one function called
//! three times, `compare_bound_rows`, and keeping them together is what makes
//! that visible to the next person to add a fourth spelling.

use inillucent_value::Collation;

use super::{comparison_rules, refused, result_collation, Binder, BoundExpr, SubqueryKind};
use crate::ast::{self, BinaryOp, Expr, ExprId, InRhs, SelectBody};
use crate::diagnostic::{ParseError, ParseErrorKind};
use crate::lexer::Span;

impl Binder<'_> {
    /// Binds `(a, b) IN (VALUES (...), (...))`.
    ///
    /// Only the value-list form, because that is what the row-value `IN` is for:
    /// a written list of tuples. `(a, b) IN (SELECT x, y FROM u)` is a
    /// correlated membership test over a query and is refused by name.
    ///
    /// @param parts - the operand row's parts
    /// @param rhs - what was written after `IN`
    /// @param negated - whether `NOT IN` was written
    /// @param span - where the test was written
    pub(super) fn bind_row_in(
        &mut self,
        parts: &[ExprId],
        rhs: &InRhs,
        negated: bool,
        span: Span,
    ) -> Result<BoundExpr, ParseError> {
        let rows = self.row_value_list(rhs).ok_or_else(|| {
            ParseError::new(
                ParseErrorKind::Unsupported("a row value IN a query rather than a value list"),
                span,
            )
        })?;
        let mut bound_lefts = Vec::with_capacity(parts.len());
        for part in parts {
            bound_lefts.push(self.bind_expr(*part)?);
        }
        let mut chain: Option<BoundExpr> = None;
        for row in &rows {
            if row.len() != parts.len() {
                return Err(ParseError::new(
                    ParseErrorKind::Refused(format!(
                        "row value misused: {} values on the left and {} on the right",
                        parts.len(),
                        row.len()
                    )),
                    span,
                ));
            }
            let mut bound_rights = Vec::with_capacity(row.len());
            for value in row {
                bound_rights.push(self.bind_expr(*value)?);
            }
            let one = equality_chain(&bound_lefts, &bound_rights);
            chain = Some(match chain {
                None => one,
                Some(held) => BoundExpr::Or(Box::new(held), Box::new(one)),
            });
        }
        // An empty list is false, and `NOT IN ()` is true, whatever the
        // operand - including a NULL one. That is SQLite's rule and it is the
        // one place `IN` is not three-valued.
        let bound = chain.unwrap_or(BoundExpr::Integer(0));
        Ok(if negated {
            BoundExpr::Not(Box::new(bound))
        } else {
            bound
        })
    }

    /// Returns the rows of a written `VALUES` list, when the right-hand side is
    /// one.
    ///
    /// @param rhs - what was written after `IN`
    fn row_value_list(&self, rhs: &InRhs) -> Option<Vec<Vec<ExprId>>> {
        match rhs {
            InRhs::Select(select) => {
                let held = self.ast.select(*select)?;
                if !held.compounds.is_empty() || !held.with.ctes.is_empty() {
                    return None;
                }
                let core = self.ast.core(held.first)?;
                match &core.body {
                    SelectBody::Values(rows) => Some(rows.clone()),
                    _ => None,
                }
            }
            // `IN ((1,2), (3,4))` is a list of row values rather than a
            // `VALUES` clause, and means the same thing.
            InRhs::List(items) => {
                let mut rows = Vec::with_capacity(items.len());
                for item in items {
                    rows.push(self.row_value_parts(*item)?);
                }
                Some(rows)
            }
            InRhs::Table { .. } => None,
        }
    }

    /// Returns the parts of a row value, or `None` when the expression is not
    /// one.
    ///
    /// @param id - the expression
    pub(super) fn row_value_parts(&self, id: ExprId) -> Option<Vec<ExprId>> {
        match self.ast.expr(id)? {
            Expr::RowValue(parts) => Some(parts.clone()),
            _ => None,
        }
    }

    /// Binds a comparison between a row value and a one-row query.
    ///
    /// **The query is bound once and read column by column.** Each part becomes
    /// its own scalar subquery over the same block with the other result
    /// columns trimmed away - which is what makes `(a, b) = (SELECT x, y ...)`
    /// mean `a = x AND b = y` over *one* row rather than two independent
    /// lookups: the block is the same block, so it plans and folds once, and
    /// `crate::subquery` answers an uncorrelated one exactly once per
    /// execution.
    ///
    /// The comparison is then the ordinary lexicographic desugaring the
    /// row-against-a-row form already uses, so `<` and `<=` mean here what they
    /// mean there.
    ///
    /// @param op - the operator
    /// @param lefts - the left row's parts
    /// @param select - the query on the right
    /// @param span - where the comparison was written
    pub(super) fn bind_row_against_query(
        &mut self,
        op: BinaryOp,
        lefts: &[ExprId],
        select: ast::SelectId,
        span: Span,
    ) -> Result<BoundExpr, ParseError> {
        let block = self.bind_value_subquery(select, span)?;
        if block.columns.len() != lefts.len() {
            return Err(refused(
                format!(
                    "row value misused: {} values on the left and {} on the right",
                    lefts.len(),
                    block.columns.len()
                ),
                span,
            ));
        }
        let mut bound_lefts = Vec::with_capacity(lefts.len());
        for part in lefts {
            bound_lefts.push(self.bind_expr(*part)?);
        }
        let mut bound_rights = Vec::with_capacity(block.columns.len());
        for at in 0..block.columns.len() {
            let mut one = block.clone();
            one.columns = block
                .columns
                .get(at..at.saturating_add(1))
                .map_or_else(Vec::new, <[crate::bind::BoundResultColumn]>::to_vec);
            let collation = one
                .columns
                .first()
                .map(|column| result_collation(&column.expr))
                .unwrap_or(Collation::Binary);
            bound_rights.push(BoundExpr::Subquery {
                id: self.next_subquery_id(),
                kind: SubqueryKind::Scalar,
                negated: false,
                operand: None,
                block: Box::new(one),
                affinity: None,
                collation,
            });
        }
        compare_bound_rows(op, &bound_lefts, &bound_rights, span)
    }

    /// Binds a comparison between two row values.
    ///
    /// @param op - the operator
    /// @param lefts - the left row's parts
    /// @param rights - the right row's parts
    /// @param span - where the comparison was written
    pub(super) fn bind_row_comparison(
        &mut self,
        op: BinaryOp,
        lefts: &[ExprId],
        rights: &[ExprId],
        span: Span,
    ) -> Result<BoundExpr, ParseError> {
        if lefts.len() != rights.len() || lefts.is_empty() {
            return Err(ParseError::new(
                ParseErrorKind::Refused(format!(
                    "row value misused: {} values on the left and {} on the right",
                    lefts.len(),
                    rights.len()
                )),
                span,
            ));
        }
        let mut bound_lefts = Vec::with_capacity(lefts.len());
        let mut bound_rights = Vec::with_capacity(rights.len());
        for (left, right) in lefts.iter().zip(rights.iter()) {
            bound_lefts.push(self.bind_expr(*left)?);
            bound_rights.push(self.bind_expr(*right)?);
        }
        match op {
            BinaryOp::Equal => Ok(equality_chain(&bound_lefts, &bound_rights)),
            // `<>` is the negation of `=` rather than an inequality of its own,
            // which is what makes `(1, NULL) <> (1, 2)` unknown rather than
            // true: the equality is unknown, and NOT of unknown is unknown.
            BinaryOp::NotEqual => Ok(BoundExpr::Not(Box::new(equality_chain(
                &bound_lefts,
                &bound_rights,
            )))),
            BinaryOp::Less | BinaryOp::LessEqual | BinaryOp::Greater | BinaryOp::GreaterEqual => {
                Ok(lexicographic_chain(op, &bound_lefts, &bound_rights, 0))
            }
            _ => Err(ParseError::new(
                ParseErrorKind::Refused("row value misused".to_string()),
                span,
            )),
        }
    }
}

/// Returns the `AND` chain that a row-value equality means.
///
/// @param lefts - the left row's parts, bound
/// @param rights - the right row's parts, bound
fn equality_chain(lefts: &[BoundExpr], rights: &[BoundExpr]) -> BoundExpr {
    let mut chain: Option<BoundExpr> = None;
    for (left, right) in lefts.iter().zip(rights.iter()) {
        let (affinity, collation) = comparison_rules(left, right);
        let one = BoundExpr::Compare {
            op: BinaryOp::Equal,
            left: Box::new(left.clone()),
            right: Box::new(right.clone()),
            affinity,
            collation,
        };
        chain = Some(match chain {
            None => one,
            Some(held) => BoundExpr::And(Box::new(held), Box::new(one)),
        });
    }
    chain.unwrap_or(BoundExpr::Null)
}

/// Returns the chain a lexicographic row-value comparison means.
///
/// `(a, b, c) < (x, y, z)` is `a < x OR (a = x AND (b < y OR (b = y AND c <
/// z)))`, and the strictness only ever applies to the last part: everything
/// before it is compared for equality to decide whether the next part matters.
///
/// @param op - the operator
/// @param lefts - the left row's parts, bound
/// @param rights - the right row's parts, bound
/// @param at - which part this level compares
fn lexicographic_chain(
    op: BinaryOp,
    lefts: &[BoundExpr],
    rights: &[BoundExpr],
    at: usize,
) -> BoundExpr {
    let (Some(left), Some(right)) = (lefts.get(at), rights.get(at)) else {
        return BoundExpr::Null;
    };
    let (affinity, collation) = comparison_rules(left, right);
    let last = at.saturating_add(1) >= lefts.len();
    // The last part carries the operator as written, including its
    // or-equal half; every earlier part is compared strictly, with the
    // equal case handled by the branch beside it.
    let strict = match op {
        BinaryOp::LessEqual if !last => BinaryOp::Less,
        BinaryOp::GreaterEqual if !last => BinaryOp::Greater,
        other => other,
    };
    let decided = BoundExpr::Compare {
        op: strict,
        left: Box::new(left.clone()),
        right: Box::new(right.clone()),
        affinity,
        collation,
    };
    if last {
        return decided;
    }
    let same = BoundExpr::Compare {
        op: BinaryOp::Equal,
        left: Box::new(left.clone()),
        right: Box::new(right.clone()),
        affinity,
        collation,
    };
    BoundExpr::Or(
        Box::new(decided),
        Box::new(BoundExpr::And(
            Box::new(same),
            Box::new(lexicographic_chain(op, lefts, rights, at.saturating_add(1))),
        )),
    )
}

/// Returns the comparison a row value against a row value means.
///
/// **One desugaring, shared by both spellings.** `=` is a chain of equalities,
/// `<>` is the negation of that chain rather than an inequality of its own -
/// which is what makes `(1, NULL) <> (1, 2)` unknown - and the ordering
/// operators are lexicographic. The row-against-a-query form binds different
/// operands and then means exactly this.
///
/// @param op - the operator
/// @param lefts - the left row, already bound
/// @param rights - the right row, already bound
/// @param span - where the comparison was written
fn compare_bound_rows(
    op: BinaryOp,
    lefts: &[BoundExpr],
    rights: &[BoundExpr],
    span: Span,
) -> Result<BoundExpr, ParseError> {
    match op {
        BinaryOp::Equal => Ok(equality_chain(lefts, rights)),
        BinaryOp::NotEqual => Ok(BoundExpr::Not(Box::new(equality_chain(lefts, rights)))),
        BinaryOp::Less | BinaryOp::LessEqual | BinaryOp::Greater | BinaryOp::GreaterEqual => {
            Ok(lexicographic_chain(op, lefts, rights, 0))
        }
        _ => Err(ParseError::new(
            ParseErrorKind::Refused("row value misused".to_string()),
            span,
        )),
    }
}