Struct DistinctOnIterator 

pub struct DistinctOnIterator<I: RowIterator> { /* private fields */ }

Iterator that implements SELECT DISTINCT ON (expr, ...).

The input is first sorted by the complete effective sort specification the planner synthesized (ON keys, user ORDER BY tail, and an all-column tie-breaker; see docs/sql-distinct-on.md D2-D4). Sorting reuses SortIterator, so spill runs are merged under the same full comparator and determinism survives external sorting. The iterator then emits only the first row of each group whose leading key_count sort keys compare equal; NULL keys compare equal to NULL (D5).

Implementations

impl<I: RowIterator> DistinctOnIterator<I>

pub fn new( input: I, order_by: &[SortExpr], key_count: usize, policy: Option<MemoryPolicy>, ) -> Result<Self>

Creates a new DISTINCT ON iterator.

order_by is the complete effective sort specification whose leading key_count entries form the distinctness key.

Errors

Returns an error if sorting the input fails.

Trait Implementations

impl<I: RowIterator> RowIterator for DistinctOnIterator<I>

fn next_row(&mut self) -> Option<Result<Row>>

Advances the iterator and returns the next row, or None if exhausted.

fn schema(&self) -> &[ColumnMetadata]

Returns the schema of rows produced by this iterator.