use crate::expression::SelectableExpression;
use crate::pg::Pg;
use crate::query_builder::order_clause::{NoOrderClause, OrderClause};
use crate::query_builder::{
AstPass, FromClause, QueryFragment, QueryId, SelectQuery, SelectStatement,
};
use crate::query_dsl::methods::DistinctOnDsl;
use crate::query_dsl::order_dsl::ValidOrderingForDistinct;
use crate::result::QueryResult;
use crate::sql_types::SingleValue;
use crate::{Expression, QuerySource};
#[derive(Debug, Clone, Copy, QueryId)]
#[cfg(feature = "postgres_backend")]
pub struct DistinctOnClause<T>(pub(crate) T);
impl<T> ValidOrderingForDistinct<DistinctOnClause<T>> for NoOrderClause {}
impl<T> ValidOrderingForDistinct<DistinctOnClause<T>> for OrderClause<(T,)> {}
impl<T> ValidOrderingForDistinct<DistinctOnClause<T>> for OrderClause<T>
where
T: Expression,
T::SqlType: SingleValue,
{
}
impl<T> ValidOrderingForDistinct<DistinctOnClause<T>> for OrderClause<crate::helper_types::Desc<T>>
where
T: Expression,
T::SqlType: SingleValue,
{
}
impl<T> ValidOrderingForDistinct<DistinctOnClause<T>> for OrderClause<crate::helper_types::Asc<T>>
where
T: Expression,
T::SqlType: SingleValue,
{
}
impl<T> ValidOrderingForDistinct<DistinctOnClause<T>>
for OrderClause<(crate::helper_types::Desc<T>,)>
where
T: Expression,
T::SqlType: SingleValue,
{
}
impl<T> ValidOrderingForDistinct<DistinctOnClause<T>>
for OrderClause<(crate::helper_types::Asc<T>,)>
where
T: Expression,
T::SqlType: SingleValue,
{
}
impl<T> QueryFragment<Pg> for DistinctOnClause<T>
where
T: QueryFragment<Pg>,
{
fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, Pg>) -> QueryResult<()> {
out.push_sql("DISTINCT ON (");
self.0.walk_ast(out.reborrow())?;
out.push_sql(")");
Ok(())
}
}
impl<ST, F, S, D, W, O, LOf, G, H, Selection> DistinctOnDsl<Selection>
for SelectStatement<FromClause<F>, S, D, W, O, LOf, G, H>
where
F: QuerySource,
Selection: SelectableExpression<F>,
Selection::SqlType: SingleValue,
Self: SelectQuery<SqlType = ST>,
O: ValidOrderingForDistinct<DistinctOnClause<Selection>>,
SelectStatement<FromClause<F>, S, DistinctOnClause<Selection>, W, O, LOf, G, H>:
SelectQuery<SqlType = ST>,
{
type Output = SelectStatement<FromClause<F>, S, DistinctOnClause<Selection>, W, O, LOf, G, H>;
fn distinct_on(self, selection: Selection) -> Self::Output {
SelectStatement::new(
self.select,
self.from,
DistinctOnClause(selection),
self.where_clause,
self.order,
self.limit_offset,
self.group_by,
self.having,
self.locking,
)
}
}