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//! The inner columns of a parenthesised join, and looking a name up among them.
//!
//! Invariant: **a name written against a parenthesised join resolves to the
//! derived column that carries the inner table's column of that name**, as it
//! does in SQLite, rather than failing because the derived table renamed it.
/// What a name matched among the inner columns of a parenthesised join.
pub(super) enum NestedHits {
/// The derived columns, by position, that carry the name.
Some(Vec<u16>),
/// Nothing carries the name, and the lookup is settled for this term.
NoneButNamed,
/// The reference names something else, such as the derived table's alias.
Unrelated,
}
/// Looks a column name up among the inner columns of a parenthesised join.
///
/// A bare name settles the lookup for the term whether or not it matched. A
/// qualified name does only when the qualifier is the name of an inner table.
///
/// @param names - where each derived column came from
/// @param column - the folded column name
/// @param qualifier - the folded qualifier, when one was written
pub(super) fn nested_hits(
names: &[NestedName],
column: &[u8],
qualifier: Option<&[u8]>,
) -> NestedHits {
let named_table = qualifier.is_none_or(|wanted| names.iter().any(|held| held.table == wanted));
if !named_table {
return NestedHits::Unrelated;
}
let hits: Vec<u16> = names
.iter()
.filter(|held| held.column == column && qualifier.is_none_or(|wanted| held.table == wanted))
.map(|held| held.index)
.collect();
if hits.is_empty() {
NestedHits::NoneButNamed
} else {
NestedHits::Some(hits)
}
}
/// Where one column of a parenthesised join came from.
#[derive(Clone, Debug, PartialEq, Eq)]
pub(crate) struct NestedName {
/// The folded name of the inner table.
pub table: Vec<u8>,
/// The folded name of the inner column.
pub column: Vec<u8>,
/// The position of the derived table's column that carries it.
pub index: u16,
}