Struct TopNResult 

pub struct TopNResult { /* private fields */ }

Top-N result using a bounded heap for ORDER BY + LIMIT optimization

This is O(n log k) instead of O(n log n) for full sort, where k = limit. For large datasets with small limits (e.g., 1M rows, LIMIT 10), this can be 5-50x faster.

Implementations

impl TopNResult

pub fn new<F>( inner: Box<dyn QueryResult>, compare: F, limit: usize, offset: usize, ) -> Result<Self>

where F: Fn(&Row, &Row) -> Ordering + Clone,

Create a new top-N result using BinaryHeap for bounded sorting

Uses a max-heap of size k (limit + offset) to efficiently find top-k elements. Only keeps k rows in memory at any time, making it memory-efficient for small limits.

Arguments

• inner - Source result to process
• compare - Comparison function for ordering (returns Less if a should come before b)
• limit - Maximum number of rows to return
• offset - Number of rows to skip (we need limit + offset rows in heap)

pub fn new_with_context<F>( inner: Box<dyn QueryResult>, compare: F, limit: usize, offset: usize, ctx: &ExecutionContext, ) -> Result<Self>

where F: Fn(&Row, &Row) -> Ordering + Clone,

pub fn from_rows_with_budget( columns: Vec<String>, rows: RowVec, budget: RetainedRowsBudget, ) -> Self

Trait Implementations

impl QueryResult for TopNResult

fn columns(&self) -> &[String]

Returns the column names in the result

fn next(&mut self) -> bool

Moves the cursor to the next row

fn scan(&self, dest: &mut [Value]) -> Result<()>

Scans the current row into the provided values

fn row(&self) -> &Row

Returns the current row directly without copying

fn take_row(&mut self) -> Row

Takes ownership of the current row (avoids clone)

fn close(&mut self) -> Result<()>

Closes the result set and releases resources

fn rows_affected(&self) -> i64

Returns the number of rows affected by an INSERT, UPDATE, or DELETE

fn last_insert_id(&self) -> i64

Returns the last inserted ID for an INSERT operation

fn with_aliases( self: Box<Self>, aliases: FxHashMap<String, String>, ) -> Box<dyn QueryResult>

Sets column aliases for this result

fn columns_arc(&self) -> Option<CompactArc<Vec<String>>>

Returns column names as Arc for zero-copy sharing

fn try_into_arc_rows(&mut self) -> Option<CompactArc<Vec<Row>>>

Try to extract all rows as CompactArc<Vec<Row>> for zero-copy joins

fn estimated_count(&self) -> Option<usize>

Returns an estimate of the total number of rows in the result.

fn supports_typed_batches(&self) -> bool

Whether the result can yield decoded typed column batches without constructing a row/value object for every result record.

fn typed_batch_fallback_reason(&self) -> Option<TypedBatchFallbackReason>

If supports_typed_batches() is false, return the best semantic reason.

fn next_typed_batch(&mut self) -> Result<Option<TypedColumnBatch>, Error>

Advance to the next typed column batch.

fn last_error(&mut self) -> Option<Error>

Returns a pending error from the last next() call, if any.