use std::{collections::HashMap, sync::Arc}; use limbo_sqlite3_parser::ast::{self, Expr, SortOrder}; use crate::{ schema::{Index, Schema}, translate::plan::TerminationKey, types::SeekOp, util::exprs_are_equivalent, Result, }; use super::plan::{ DeletePlan, Direction, GroupBy, IterationDirection, Operation, Plan, Search, SeekDef, SeekKey, SelectPlan, TableReference, UpdatePlan, WhereTerm, }; pub fn optimize_plan(plan: &mut Plan, schema: &Schema) -> Result<()> { match plan { Plan::Select(plan) => optimize_select_plan(plan, schema), Plan::Delete(plan) => optimize_delete_plan(plan, schema), Plan::Update(plan) => optimize_update_plan(plan, schema), } } /** * Make a few passes over the plan to optimize it. * TODO: these could probably be done in less passes, * but having them separate makes them easier to understand */ fn optimize_select_plan(plan: &mut SelectPlan, schema: &Schema) -> Result<()> { optimize_subqueries(plan, schema)?; rewrite_exprs_select(plan)?; if let ConstantConditionEliminationResult::ImpossibleCondition = eliminate_constant_conditions(&mut plan.where_clause)? { plan.contains_constant_false_condition = true; return Ok(()); } use_indexes( &mut plan.table_references, &schema.indexes, &mut plan.where_clause, &mut plan.order_by, &plan.group_by, )?; eliminate_orderby_like_groupby(plan)?; Ok(()) } fn optimize_delete_plan(plan: &mut DeletePlan, schema: &Schema) -> Result<()> { rewrite_exprs_delete(plan)?; if let ConstantConditionEliminationResult::ImpossibleCondition = eliminate_constant_conditions(&mut plan.where_clause)? { plan.contains_constant_false_condition = true; return Ok(()); } use_indexes( &mut plan.table_references, &schema.indexes, &mut plan.where_clause, &mut plan.order_by, &None, )?; Ok(()) } fn optimize_update_plan(plan: &mut UpdatePlan, schema: &Schema) -> Result<()> { rewrite_exprs_update(plan)?; if let ConstantConditionEliminationResult::ImpossibleCondition = eliminate_constant_conditions(&mut plan.where_clause)? { plan.contains_constant_false_condition = true; return Ok(()); } use_indexes( &mut plan.table_references, &schema.indexes, &mut plan.where_clause, &mut plan.order_by, &None, )?; Ok(()) } fn optimize_subqueries(plan: &mut SelectPlan, schema: &Schema) -> Result<()> { for table in plan.table_references.iter_mut() { if let Operation::Subquery { plan, .. } = &mut table.op { optimize_select_plan(&mut *plan, schema)?; } } Ok(()) } fn eliminate_orderby_like_groupby(plan: &mut SelectPlan) -> Result<()> { if plan.order_by.is_none() | plan.group_by.is_none() { return Ok(()); } if plan.table_references.len() == 0 { return Ok(()); } let order_by_clauses = plan.order_by.as_mut().unwrap(); let group_by_clauses = plan.group_by.as_mut().unwrap(); let mut group_by_insert_position = 0; let mut order_index = 0; // This function optimizes query execution by eliminating duplicate expressions between ORDER BY and GROUP BY clauses // When the same column appears in both clauses, we can avoid redundant sorting operations // The function reorders GROUP BY expressions and removes redundant ORDER BY expressions to ensure consistent ordering while order_index < order_by_clauses.len() { let (order_expr, direction) = &order_by_clauses[order_index]; // Skip descending orders as they require separate sorting if matches!(direction, Direction::Descending) { order_index += 1; continue; } // Check if the current ORDER BY expression matches any expression in the GROUP BY clause if let Some(group_expr_position) = group_by_clauses .exprs .iter() .position(|expr| exprs_are_equivalent(expr, order_expr)) { // If we found a matching expression in GROUP BY, we need to ensure it's in the correct position // to preserve the ordering specified by ORDER BY clauses // Move the matching GROUP BY expression to the current insertion position // This effectively "bubbles up" the expression to maintain proper ordering if group_expr_position != group_by_insert_position { let mut current_position = group_expr_position; // Swap expressions to move the matching one to the correct position while current_position > group_by_insert_position { group_by_clauses .exprs .swap(current_position, current_position - 1); current_position -= 1; } } group_by_insert_position += 1; // Remove this expression from ORDER BY since it's now handled by GROUP BY order_by_clauses.remove(order_index); // Note: We don't increment order_index here because removal shifts all elements } else { // If not found in GROUP BY, move to next ORDER BY expression order_index += 1; } } if order_by_clauses.is_empty() { plan.order_by = None } Ok(()) } fn eliminate_unnecessary_orderby( table_references: &mut [TableReference], available_indexes: &HashMap>>, order_by: &mut Option>, group_by: &Option, ) -> Result<()> { let Some(order) = order_by else { return Ok(()); }; let Some(first_table_reference) = table_references.first_mut() else { return Ok(()); }; let Some(btree_table) = first_table_reference.btree() else { return Ok(()); }; // If GROUP BY clause is present, we can't rely on already ordered columns because GROUP BY reorders the data // This early return prevents the elimination of ORDER BY when GROUP BY exists, as sorting must be applied after grouping // And if ORDER BY clause duplicates GROUP BY we handle it later in fn eliminate_orderby_like_groupby if group_by.is_some() { return Ok(()); } let Operation::Scan { index, iter_dir, .. } = &mut first_table_reference.op else { return Ok(()); }; assert!( index.is_none(), "Nothing shouldve transformed the scan to use an index yet" ); // Special case: if ordering by just the rowid, we can remove the ORDER BY clause if order.len() == 1 && order[0].0.is_rowid_alias_of(0) { *iter_dir = match order[0].1 { Direction::Ascending => IterationDirection::Forwards, Direction::Descending => IterationDirection::Backwards, }; *order_by = None; return Ok(()); } // Find the best matching index for the ORDER BY columns let table_name = &btree_table.name; let mut best_index = (None, 0); for (_, indexes) in available_indexes.iter() { for index_candidate in indexes.iter().filter(|i| &i.table_name == table_name) { let matching_columns = index_candidate.columns.iter().enumerate().take_while(|(i, c)| { if let Some((Expr::Column { table, column, .. }, _)) = order.get(*i) { let col_idx_in_table = btree_table .columns .iter() .position(|tc| tc.name.as_ref() == Some(&c.name)); matches!(col_idx_in_table, Some(col_idx) if *table == 0 && *column == col_idx) } else { false } }).count(); if matching_columns > best_index.1 { best_index = (Some(index_candidate), matching_columns); } } } let Some(matching_index) = best_index.0 else { return Ok(()); }; let match_count = best_index.1; // If we found a matching index, use it for scanning *index = Some(matching_index.clone()); // If the order by direction matches the index direction, we can iterate the index in forwards order. // If they don't, we must iterate the index in backwards order. let index_direction = &matching_index.columns.first().as_ref().unwrap().order; *iter_dir = match (index_direction, order[0].1) { (SortOrder::Asc, Direction::Ascending) | (SortOrder::Desc, Direction::Descending) => { IterationDirection::Forwards } (SortOrder::Asc, Direction::Descending) | (SortOrder::Desc, Direction::Ascending) => { IterationDirection::Backwards } }; // If the index covers all ORDER BY columns, and one of the following applies: // - the ORDER BY directions exactly match the index orderings, // - the ORDER by directions are the exact opposite of the index orderings, // we can remove the ORDER BY clause. if match_count == order.len() { let full_match = { let mut all_match_forward = true; let mut all_match_reverse = true; for (i, (_, direction)) in order.iter().enumerate() { match (&matching_index.columns[i].order, direction) { (SortOrder::Asc, Direction::Ascending) | (SortOrder::Desc, Direction::Descending) => { all_match_reverse = false; } (SortOrder::Asc, Direction::Descending) | (SortOrder::Desc, Direction::Ascending) => { all_match_forward = false; } } } all_match_forward || all_match_reverse }; if full_match { *order_by = None; } } Ok(()) } /** * Use indexes where possible. * * When this function is called, condition expressions from both the actual WHERE clause and the JOIN clauses are in the where_clause vector. * If we find a condition that can be used to index scan, we pop it off from the where_clause vector and put it into a Search operation. * We put it there simply because it makes it a bit easier to track during translation. * * In this function we also try to eliminate ORDER BY clauses if there is an index that satisfies the ORDER BY clause. */ fn use_indexes( table_references: &mut [TableReference], available_indexes: &HashMap>>, where_clause: &mut Vec, order_by: &mut Option>, group_by: &Option, ) -> Result<()> { // Try to use indexes for eliminating ORDER BY clauses eliminate_unnecessary_orderby(table_references, available_indexes, order_by, group_by)?; // Try to use indexes for WHERE conditions for (table_index, table_reference) in table_references.iter_mut().enumerate() { if matches!(table_reference.op, Operation::Scan { .. }) { let index = if let Operation::Scan { index, .. } = &table_reference.op { Option::clone(index) } else { None }; match index { // If we decided to eliminate ORDER BY using an index, let's constrain our search to only that index Some(index) => { let available_indexes = available_indexes .values() .flatten() .filter(|i| i.name == index.name) .cloned() .collect::>(); if let Some(search) = try_extract_index_search_from_where_clause( where_clause, table_index, table_reference, &available_indexes, )? { table_reference.op = Operation::Search(search); } } None => { let table_name = table_reference.table.get_name(); // If we can utilize the rowid alias of the table, let's preferentially always use it for now. let mut i = 0; while i < where_clause.len() { if let Some(search) = try_extract_rowid_search_expression( &mut where_clause[i], table_index, table_reference, )? { where_clause.remove(i); table_reference.op = Operation::Search(search); continue; } else { i += 1; } } if let Some(indexes) = available_indexes.get(table_name) { if let Some(search) = try_extract_index_search_from_where_clause( where_clause, table_index, table_reference, indexes, )? { table_reference.op = Operation::Search(search); } } } } } } Ok(()) } #[derive(Debug, PartialEq, Clone)] enum ConstantConditionEliminationResult { Continue, ImpossibleCondition, } /// Removes predicates that are always true. /// Returns a ConstantEliminationResult indicating whether any predicates are always false. /// This is used to determine whether the query can be aborted early. fn eliminate_constant_conditions( where_clause: &mut Vec, ) -> Result { let mut i = 0; while i < where_clause.len() { let predicate = &where_clause[i]; if predicate.expr.is_always_true()? { // true predicates can be removed since they don't affect the result where_clause.remove(i); } else if predicate.expr.is_always_false()? { // any false predicate in a list of conjuncts (AND-ed predicates) will make the whole list false, // except an outer join condition, because that just results in NULLs, not skipping the whole loop if predicate.from_outer_join { i += 1; continue; } where_clause.truncate(0); return Ok(ConstantConditionEliminationResult::ImpossibleCondition); } else { i += 1; } } Ok(ConstantConditionEliminationResult::Continue) } fn rewrite_exprs_select(plan: &mut SelectPlan) -> Result<()> { for rc in plan.result_columns.iter_mut() { rewrite_expr(&mut rc.expr)?; } for agg in plan.aggregates.iter_mut() { rewrite_expr(&mut agg.original_expr)?; } for cond in plan.where_clause.iter_mut() { rewrite_expr(&mut cond.expr)?; } if let Some(group_by) = &mut plan.group_by { for expr in group_by.exprs.iter_mut() { rewrite_expr(expr)?; } } if let Some(order_by) = &mut plan.order_by { for (expr, _) in order_by.iter_mut() { rewrite_expr(expr)?; } } Ok(()) } fn rewrite_exprs_delete(plan: &mut DeletePlan) -> Result<()> { for cond in plan.where_clause.iter_mut() { rewrite_expr(&mut cond.expr)?; } Ok(()) } fn rewrite_exprs_update(plan: &mut UpdatePlan) -> Result<()> { if let Some(rc) = plan.returning.as_mut() { for rc in rc.iter_mut() { rewrite_expr(&mut rc.expr)?; } } for (_, expr) in plan.set_clauses.iter_mut() { rewrite_expr(expr)?; } for cond in plan.where_clause.iter_mut() { rewrite_expr(&mut cond.expr)?; } if let Some(order_by) = &mut plan.order_by { for (expr, _) in order_by.iter_mut() { rewrite_expr(expr)?; } } Ok(()) } #[derive(Debug, Clone, Copy, PartialEq, Eq)] pub enum ConstantPredicate { AlwaysTrue, AlwaysFalse, } /** Helper trait for expressions that can be optimized Implemented for ast::Expr */ pub trait Optimizable { // if the expression is a constant expression e.g. '1', returns the constant condition fn check_constant(&self) -> Result>; fn is_always_true(&self) -> Result { Ok(self .check_constant()? .map_or(false, |c| c == ConstantPredicate::AlwaysTrue)) } fn is_always_false(&self) -> Result { Ok(self .check_constant()? .map_or(false, |c| c == ConstantPredicate::AlwaysFalse)) } fn is_rowid_alias_of(&self, table_index: usize) -> bool; fn is_nonnull(&self) -> bool; } impl Optimizable for ast::Expr { fn is_rowid_alias_of(&self, table_index: usize) -> bool { match self { Self::Column { table, is_rowid_alias, .. } => *is_rowid_alias && *table == table_index, _ => false, } } /// Returns true if the expressions is (verifiably) non-NULL. /// It might still be non-NULL even if we return false; we just /// weren't able to prove it. /// This function is currently very conservative, and will return false /// for any expression where we aren't sure and didn't bother to find out /// by writing more complex code. fn is_nonnull(&self) -> bool { match self { Expr::Between { lhs, start, end, .. } => lhs.is_nonnull() && start.is_nonnull() && end.is_nonnull(), Expr::Binary(expr, _, expr1) => expr.is_nonnull() && expr1.is_nonnull(), Expr::Case { base, when_then_pairs, else_expr, .. } => { base.as_ref().map_or(true, |base| base.is_nonnull()) && when_then_pairs.iter().all(|(_, then)| then.is_nonnull()) && else_expr .as_ref() .map_or(true, |else_expr| else_expr.is_nonnull()) } Expr::Cast { expr, .. } => expr.is_nonnull(), Expr::Collate(expr, _) => expr.is_nonnull(), Expr::DoublyQualified(..) => { panic!("Do not call is_nonnull before DoublyQualified has been rewritten as Column") } Expr::Exists(..) => false, Expr::FunctionCall { .. } => false, Expr::FunctionCallStar { .. } => false, Expr::Id(..) => panic!("Do not call is_nonnull before Id has been rewritten as Column"), Expr::Column { is_rowid_alias, .. } => *is_rowid_alias, Expr::RowId { .. } => true, Expr::InList { lhs, rhs, .. } => { lhs.is_nonnull() && rhs .as_ref() .map_or(true, |rhs| rhs.iter().all(|rhs| rhs.is_nonnull())) } Expr::InSelect { .. } => false, Expr::InTable { .. } => false, Expr::IsNull(..) => true, Expr::Like { lhs, rhs, .. } => lhs.is_nonnull() && rhs.is_nonnull(), Expr::Literal(literal) => match literal { ast::Literal::Numeric(_) => true, ast::Literal::String(_) => true, ast::Literal::Blob(_) => true, ast::Literal::Keyword(_) => true, ast::Literal::Null => false, ast::Literal::CurrentDate => true, ast::Literal::CurrentTime => true, ast::Literal::CurrentTimestamp => true, }, Expr::Name(..) => false, Expr::NotNull(..) => true, Expr::Parenthesized(exprs) => exprs.iter().all(|expr| expr.is_nonnull()), Expr::Qualified(..) => { panic!("Do not call is_nonnull before Qualified has been rewritten as Column") } Expr::Raise(..) => false, Expr::Subquery(..) => false, Expr::Unary(_, expr) => expr.is_nonnull(), Expr::Variable(..) => false, } } fn check_constant(&self) -> Result> { match self { Self::Literal(lit) => match lit { ast::Literal::Numeric(b) => { if let Ok(int_value) = b.parse::() { return Ok(Some(if int_value == 0 { ConstantPredicate::AlwaysFalse } else { ConstantPredicate::AlwaysTrue })); } if let Ok(float_value) = b.parse::() { return Ok(Some(if float_value == 0.0 { ConstantPredicate::AlwaysFalse } else { ConstantPredicate::AlwaysTrue })); } Ok(None) } ast::Literal::String(s) => { let without_quotes = s.trim_matches('\''); if let Ok(int_value) = without_quotes.parse::() { return Ok(Some(if int_value == 0 { ConstantPredicate::AlwaysFalse } else { ConstantPredicate::AlwaysTrue })); } if let Ok(float_value) = without_quotes.parse::() { return Ok(Some(if float_value == 0.0 { ConstantPredicate::AlwaysFalse } else { ConstantPredicate::AlwaysTrue })); } Ok(Some(ConstantPredicate::AlwaysFalse)) } _ => Ok(None), }, Self::Unary(op, expr) => { if *op == ast::UnaryOperator::Not { let trivial = expr.check_constant()?; return Ok(trivial.map(|t| match t { ConstantPredicate::AlwaysTrue => ConstantPredicate::AlwaysFalse, ConstantPredicate::AlwaysFalse => ConstantPredicate::AlwaysTrue, })); } if *op == ast::UnaryOperator::Negative { let trivial = expr.check_constant()?; return Ok(trivial); } Ok(None) } Self::InList { lhs: _, not, rhs } => { if rhs.is_none() { return Ok(Some(if *not { ConstantPredicate::AlwaysTrue } else { ConstantPredicate::AlwaysFalse })); } let rhs = rhs.as_ref().unwrap(); if rhs.is_empty() { return Ok(Some(if *not { ConstantPredicate::AlwaysTrue } else { ConstantPredicate::AlwaysFalse })); } Ok(None) } Self::Binary(lhs, op, rhs) => { let lhs_trivial = lhs.check_constant()?; let rhs_trivial = rhs.check_constant()?; match op { ast::Operator::And => { if lhs_trivial == Some(ConstantPredicate::AlwaysFalse) || rhs_trivial == Some(ConstantPredicate::AlwaysFalse) { return Ok(Some(ConstantPredicate::AlwaysFalse)); } if lhs_trivial == Some(ConstantPredicate::AlwaysTrue) && rhs_trivial == Some(ConstantPredicate::AlwaysTrue) { return Ok(Some(ConstantPredicate::AlwaysTrue)); } Ok(None) } ast::Operator::Or => { if lhs_trivial == Some(ConstantPredicate::AlwaysTrue) || rhs_trivial == Some(ConstantPredicate::AlwaysTrue) { return Ok(Some(ConstantPredicate::AlwaysTrue)); } if lhs_trivial == Some(ConstantPredicate::AlwaysFalse) && rhs_trivial == Some(ConstantPredicate::AlwaysFalse) { return Ok(Some(ConstantPredicate::AlwaysFalse)); } Ok(None) } _ => Ok(None), } } _ => Ok(None), } } } fn opposite_cmp_op(op: ast::Operator) -> ast::Operator { match op { ast::Operator::Equals => ast::Operator::Equals, ast::Operator::Greater => ast::Operator::Less, ast::Operator::GreaterEquals => ast::Operator::LessEquals, ast::Operator::Less => ast::Operator::Greater, ast::Operator::LessEquals => ast::Operator::GreaterEquals, _ => panic!("unexpected operator: {:?}", op), } } /// Struct used for scoring index scans /// Currently we just score by the number of index columns that can be utilized /// in the scan, i.e. no statistics are used. struct IndexScore { index: Option>, score: usize, constraints: Vec, } /// Try to extract an index search from the WHERE clause /// Returns an optional [Search] struct if an index search can be extracted, otherwise returns None. pub fn try_extract_index_search_from_where_clause( where_clause: &mut Vec, table_index: usize, table_reference: &TableReference, table_indexes: &[Arc], ) -> Result> { // If there are no WHERE terms, we can't extract a search if where_clause.is_empty() { return Ok(None); } // If there are no indexes, we can't extract a search if table_indexes.is_empty() { return Ok(None); } let iter_dir = if let Operation::Scan { iter_dir, .. } = &table_reference.op { *iter_dir } else { return Ok(None); }; // Find all potential index constraints // For WHERE terms to be used to constrain an index scan, they must: // 1. refer to columns in the table that the index is on // 2. be a binary comparison expression // 3. constrain the index columns in the order that they appear in the index // - e.g. if the index is on (a,b,c) then we can use all of "a = 1 AND b = 2 AND c = 3" to constrain the index scan, // - but if the where clause is "a = 1 and c = 3" then we can only use "a = 1". let mut constraints_cur = vec![]; let mut best_index = IndexScore { index: None, score: 0, constraints: vec![], }; for index in table_indexes { // Check how many terms in the where clause constrain the index in column order find_index_constraints( where_clause, table_index, table_reference, index, &mut constraints_cur, )?; // naive scoring since we don't have statistics: prefer the index where we can use the most columns // e.g. if we can use all columns of an index on (a,b), it's better than an index of (c,d,e) where we can only use c. let score = constraints_cur.len(); if score > best_index.score { best_index.index = Some(Arc::clone(index)); best_index.score = score; best_index.constraints.clear(); best_index.constraints.append(&mut constraints_cur); } } if best_index.index.is_none() { return Ok(None); } // Build the seek definition let seek_def = build_seek_def_from_index_constraints(&best_index.constraints, iter_dir, where_clause)?; // Remove the used terms from the where_clause since they are now part of the seek definition // Sort terms by position in descending order to avoid shifting indices during removal best_index.constraints.sort_by(|a, b| { b.position_in_where_clause .0 .cmp(&a.position_in_where_clause.0) }); for constraint in best_index.constraints.iter() { where_clause.remove(constraint.position_in_where_clause.0); } return Ok(Some(Search::Seek { index: best_index.index, seek_def, })); } #[derive(Debug, Clone)] /// A representation of an expression in a [WhereTerm] that can potentially be used as part of an index seek key. /// For example, if there is an index on table T(x,y) and another index on table U(z), and the where clause is "WHERE x > 10 AND 20 = z", /// the index constraints are: /// - x > 10 ==> IndexConstraint { position_in_where_clause: (0, [BinaryExprSide::Rhs]), operator: [ast::Operator::Greater] } /// - 20 = z ==> IndexConstraint { position_in_where_clause: (1, [BinaryExprSide::Lhs]), operator: [ast::Operator::Equals] } pub struct IndexConstraint { position_in_where_clause: (usize, BinaryExprSide), operator: ast::Operator, } /// Helper enum for [IndexConstraint] to indicate which side of a binary comparison expression is being compared to the index column. /// For example, if the where clause is "WHERE x = 10" and there's an index on x, /// the [IndexConstraint] for the where clause term "x = 10" will have a [BinaryExprSide::Rhs] /// because the right hand side expression "10" is being compared to the index column "x". #[derive(Debug, Clone, Copy, PartialEq, Eq)] enum BinaryExprSide { Lhs, Rhs, } /// Get the position of a column in an index /// For example, if there is an index on table T(x,y) then y's position in the index is 1. fn get_column_position_in_index( expr: &ast::Expr, table_index: usize, table_reference: &TableReference, index: &Arc, ) -> Option { let ast::Expr::Column { table, column, .. } = expr else { return None; }; if *table != table_index { return None; } let Some(column) = table_reference.table.get_column_at(*column) else { return None; }; index .columns .iter() .position(|col| Some(&col.name) == column.name.as_ref()) } /// Find all [IndexConstraint]s for a given WHERE clause /// Constraints are appended as long as they constrain the index in column order. /// E.g. for index (a,b,c) to be fully used, there must be a [WhereTerm] for each of a, b, and c. /// If e.g. only a and c are present, then only the first column 'a' of the index will be used. fn find_index_constraints( where_clause: &mut Vec, table_index: usize, table_reference: &TableReference, index: &Arc, out_constraints: &mut Vec, ) -> Result<()> { for position_in_index in 0..index.columns.len() { let mut found = false; for (position_in_where_clause, term) in where_clause.iter().enumerate() { // Skip terms that cannot be evaluated at this table's loop level if !term.should_eval_at_loop(table_index) { continue; } // Skip terms that are not binary comparisons let ast::Expr::Binary(lhs, operator, rhs) = &term.expr else { continue; }; // Only consider index scans for binary ops that are comparisons if !matches!( *operator, ast::Operator::Equals | ast::Operator::Greater | ast::Operator::GreaterEquals | ast::Operator::Less | ast::Operator::LessEquals ) { continue; } // Check if lhs is a column that is in the i'th position of the index if Some(position_in_index) == get_column_position_in_index(lhs, table_index, table_reference, index) { out_constraints.push(IndexConstraint { operator: *operator, position_in_where_clause: (position_in_where_clause, BinaryExprSide::Rhs), }); found = true; break; } // Check if rhs is a column that is in the i'th position of the index if Some(position_in_index) == get_column_position_in_index(rhs, table_index, table_reference, index) { out_constraints.push(IndexConstraint { operator: opposite_cmp_op(*operator), // swap the operator since e.g. if condition is 5 >= x, we want to use x <= 5 position_in_where_clause: (position_in_where_clause, BinaryExprSide::Lhs), }); found = true; break; } } if !found { // Expressions must constrain index columns in index definition order. If we didn't find a constraint for the i'th index column, // then we stop here and return the constraints we have found so far. break; } } // In a multicolumn index, only the last term can have a nonequality expression. // For example, imagine an index on (x,y) and the where clause is "WHERE x > 10 AND y > 20"; // We can't use GT(x: 10,y: 20) as the seek key, because the first row greater than (x: 10,y: 20) // might be e.g. (x: 10,y: 21), which does not satisfy the where clause, but a row after that e.g. (x: 11,y: 21) does. // So: // - in this case only GT(x: 10) can be used as the seek key, and we must emit a regular condition expression for y > 20 while scanning. // On the other hand, if the where clause is "WHERE x = 10 AND y > 20", we can use GT(x=10,y=20) as the seek key, // because any rows where (x=10,y=20) < ROW < (x=11) will match the where clause. for i in 0..out_constraints.len() { if out_constraints[i].operator != ast::Operator::Equals { out_constraints.truncate(i + 1); break; } } Ok(()) } /// Build a [SeekDef] for a given list of [IndexConstraint]s pub fn build_seek_def_from_index_constraints( constraints: &[IndexConstraint], iter_dir: IterationDirection, where_clause: &mut Vec, ) -> Result { assert!( !constraints.is_empty(), "cannot build seek def from empty list of index constraints" ); // Extract the key values and operators let mut key = Vec::with_capacity(constraints.len()); for constraint in constraints { // Extract the other expression from the binary WhereTerm (i.e. the one being compared to the index column) let (idx, side) = constraint.position_in_where_clause; let where_term = &mut where_clause[idx]; let ast::Expr::Binary(lhs, _, rhs) = where_term.expr.take_ownership() else { crate::bail_parse_error!("expected binary expression"); }; let cmp_expr = if side == BinaryExprSide::Lhs { *lhs } else { *rhs }; key.push(cmp_expr); } // We know all but potentially the last term is an equality, so we can use the operator of the last term // to form the SeekOp let op = constraints.last().unwrap().operator; build_seek_def(op, iter_dir, key) } /// Build a [SeekDef] for a given comparison operator and index key. /// To be usable as a seek key, all but potentially the last term must be equalities. /// The last term can be a nonequality. /// The comparison operator referred to by `op` is the operator of the last term. /// /// There are two parts to the seek definition: /// 1. The [SeekKey], which specifies the key that we will use to seek to the first row that matches the index key. /// 2. The [TerminationKey], which specifies the key that we will use to terminate the index scan that follows the seek. /// /// There are some nuances to how, and which parts of, the index key can be used in the [SeekKey] and [TerminationKey], /// depending on the operator and iteration direction. This function explains those nuances inline when dealing with /// each case. /// /// But to illustrate the general idea, consider the following examples: /// /// 1. For example, having two conditions like (x>10 AND y>20) cannot be used as a valid [SeekKey] GT(x:10, y:20) /// because the first row greater than (x:10, y:20) might be (x:10, y:21), which does not satisfy the where clause. /// In this case, only GT(x:10) must be used as the [SeekKey], and rows with y <= 20 must be filtered as a regular condition expression for each value of x. /// /// 2. In contrast, having (x=10 AND y>20) forms a valid index key GT(x:10, y:20) because after the seek, we can simply terminate as soon as x > 10, /// i.e. use GT(x:10, y:20) as the [SeekKey] and GT(x:10) as the [TerminationKey]. /// fn build_seek_def( op: ast::Operator, iter_dir: IterationDirection, key: Vec, ) -> Result { let key_len = key.len(); Ok(match (iter_dir, op) { // Forwards, EQ: // Example: (x=10 AND y=20) // Seek key: GE(x:10, y:20) // Termination key: GT(x:10, y:20) (IterationDirection::Forwards, ast::Operator::Equals) => SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len, op: SeekOp::GE, }), termination: Some(TerminationKey { len: key_len, op: SeekOp::GT, }), }, // Forwards, GT: // Example: (x=10 AND y>20) // Seek key: GT(x:10, y:20) // Termination key: GT(x:10) (IterationDirection::Forwards, ast::Operator::Greater) => { let termination_key_len = key_len - 1; SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len, op: SeekOp::GT, }), termination: if termination_key_len > 0 { Some(TerminationKey { len: termination_key_len, op: SeekOp::GT, }) } else { None }, } } // Forwards, GE: // Example: (x=10 AND y>=20) // Seek key: GE(x:10, y:20) // Termination key: GT(x:10) (IterationDirection::Forwards, ast::Operator::GreaterEquals) => { let termination_key_len = key_len - 1; SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len, op: SeekOp::GE, }), termination: if termination_key_len > 0 { Some(TerminationKey { len: termination_key_len, op: SeekOp::GT, }) } else { None }, } } // Forwards, LT: // Example: (x=10 AND y<20) // Seek key: GT(x:10, y: NULL) // NULL is always LT, indicating we only care about x // Termination key: GE(x:10, y:20) (IterationDirection::Forwards, ast::Operator::Less) => SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len - 1, op: SeekOp::GT, }), termination: Some(TerminationKey { len: key_len, op: SeekOp::GE, }), }, // Forwards, LE: // Example: (x=10 AND y<=20) // Seek key: GE(x:10, y:NULL) // NULL is always LT, indicating we only care about x // Termination key: GT(x:10, y:20) (IterationDirection::Forwards, ast::Operator::LessEquals) => SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len - 1, op: SeekOp::GE, }), termination: Some(TerminationKey { len: key_len, op: SeekOp::GT, }), }, // Backwards, EQ: // Example: (x=10 AND y=20) // Seek key: LE(x:10, y:20) // Termination key: LT(x:10, y:20) (IterationDirection::Backwards, ast::Operator::Equals) => SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len, op: SeekOp::LE, }), termination: Some(TerminationKey { len: key_len, op: SeekOp::LT, }), }, // Backwards, LT: // Example: (x=10 AND y<20) // Seek key: LT(x:10, y:20) // Termination key: LT(x:10) (IterationDirection::Backwards, ast::Operator::Less) => { let termination_key_len = key_len - 1; SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len, op: SeekOp::LT, }), termination: if termination_key_len > 0 { Some(TerminationKey { len: termination_key_len, op: SeekOp::LT, }) } else { None }, } } // Backwards, LE: // Example: (x=10 AND y<=20) // Seek key: LE(x:10, y:20) // Termination key: LT(x:10) (IterationDirection::Backwards, ast::Operator::LessEquals) => { let termination_key_len = key_len - 1; SeekDef { key, iter_dir, seek: Some(SeekKey { len: key_len, op: SeekOp::LE, }), termination: if termination_key_len > 0 { Some(TerminationKey { len: termination_key_len, op: SeekOp::LT, }) } else { None }, } } // Backwards, GT: // Example: (x=10 AND y>20) // Seek key: LE(x:10) // try to find the last row where x = 10, not considering y at all. // Termination key: LE(x:10, y:20) (IterationDirection::Backwards, ast::Operator::Greater) => { let seek_key_len = key_len - 1; SeekDef { key, iter_dir, seek: if seek_key_len > 0 { Some(SeekKey { len: seek_key_len, op: SeekOp::LE, }) } else { None }, termination: Some(TerminationKey { len: key_len, op: SeekOp::LE, }), } } // Backwards, GE: // Example: (x=10 AND y>=20) // Seek key: LE(x:10) // try to find the last row where x = 10, not considering y at all. // Termination key: LT(x:10, y:20) (IterationDirection::Backwards, ast::Operator::GreaterEquals) => { let seek_key_len = key_len - 1; SeekDef { key, iter_dir, seek: if seek_key_len > 0 { Some(SeekKey { len: seek_key_len, op: SeekOp::LE, }) } else { None }, termination: Some(TerminationKey { len: key_len, op: SeekOp::LT, }), } } (_, op) => { crate::bail_parse_error!("build_seek_def: invalid operator: {:?}", op,) } }) } pub fn try_extract_rowid_search_expression( cond: &mut WhereTerm, table_index: usize, table_reference: &TableReference, ) -> Result> { let iter_dir = if let Operation::Scan { iter_dir, .. } = &table_reference.op { *iter_dir } else { return Ok(None); }; if !cond.should_eval_at_loop(table_index) { return Ok(None); } match &mut cond.expr { ast::Expr::Binary(lhs, operator, rhs) => { if lhs.is_rowid_alias_of(table_index) { match operator { ast::Operator::Equals => { let rhs_owned = rhs.take_ownership(); return Ok(Some(Search::RowidEq { cmp_expr: WhereTerm { expr: rhs_owned, from_outer_join: cond.from_outer_join, eval_at: cond.eval_at, }, })); } ast::Operator::Greater | ast::Operator::GreaterEquals | ast::Operator::Less | ast::Operator::LessEquals => { let rhs_owned = rhs.take_ownership(); let seek_def = build_seek_def(*operator, iter_dir, vec![rhs_owned])?; return Ok(Some(Search::Seek { index: None, seek_def, })); } _ => {} } } if rhs.is_rowid_alias_of(table_index) { match operator { ast::Operator::Equals => { let lhs_owned = lhs.take_ownership(); return Ok(Some(Search::RowidEq { cmp_expr: WhereTerm { expr: lhs_owned, from_outer_join: cond.from_outer_join, eval_at: cond.eval_at, }, })); } ast::Operator::Greater | ast::Operator::GreaterEquals | ast::Operator::Less | ast::Operator::LessEquals => { let lhs_owned = lhs.take_ownership(); let op = opposite_cmp_op(*operator); let seek_def = build_seek_def(op, iter_dir, vec![lhs_owned])?; return Ok(Some(Search::Seek { index: None, seek_def, })); } _ => {} } } Ok(None) } _ => Ok(None), } } fn rewrite_expr(expr: &mut ast::Expr) -> Result<()> { match expr { ast::Expr::Id(id) => { // Convert "true" and "false" to 1 and 0 if id.0.eq_ignore_ascii_case("true") { *expr = ast::Expr::Literal(ast::Literal::Numeric(1.to_string())); return Ok(()); } if id.0.eq_ignore_ascii_case("false") { *expr = ast::Expr::Literal(ast::Literal::Numeric(0.to_string())); return Ok(()); } Ok(()) } ast::Expr::Between { lhs, not, start, end, } => { // Convert `y NOT BETWEEN x AND z` to `x > y OR y > z` let (lower_op, upper_op) = if *not { (ast::Operator::Greater, ast::Operator::Greater) } else { // Convert `y BETWEEN x AND z` to `x <= y AND y <= z` (ast::Operator::LessEquals, ast::Operator::LessEquals) }; rewrite_expr(start)?; rewrite_expr(lhs)?; rewrite_expr(end)?; let start = start.take_ownership(); let lhs = lhs.take_ownership(); let end = end.take_ownership(); let lower_bound = ast::Expr::Binary(Box::new(start), lower_op, Box::new(lhs.clone())); let upper_bound = ast::Expr::Binary(Box::new(lhs), upper_op, Box::new(end)); if *not { *expr = ast::Expr::Binary( Box::new(lower_bound), ast::Operator::Or, Box::new(upper_bound), ); } else { *expr = ast::Expr::Binary( Box::new(lower_bound), ast::Operator::And, Box::new(upper_bound), ); } Ok(()) } ast::Expr::Parenthesized(ref mut exprs) => { for subexpr in exprs.iter_mut() { rewrite_expr(subexpr)?; } let exprs = std::mem::take(exprs); *expr = ast::Expr::Parenthesized(exprs); Ok(()) } // Process other expressions recursively ast::Expr::Binary(lhs, _, rhs) => { rewrite_expr(lhs)?; rewrite_expr(rhs)?; Ok(()) } ast::Expr::FunctionCall { args, .. } => { if let Some(args) = args { for arg in args.iter_mut() { rewrite_expr(arg)?; } } Ok(()) } ast::Expr::Unary(_, arg) => { rewrite_expr(arg)?; Ok(()) } _ => Ok(()), } } trait TakeOwnership { fn take_ownership(&mut self) -> Self; } impl TakeOwnership for ast::Expr { fn take_ownership(&mut self) -> Self { std::mem::replace(self, ast::Expr::Literal(ast::Literal::Null)) } }