Struct Exists 

#[non_exhaustive]
pub struct Exists<T> {
    pub subselect: Subselect<T, Bool>,
}

Available on crate feature i-implement-a-third-party-backend-and-opt-into-breaking-changes only.

The query dsl node that represents a SQL EXISTS (subselect) expression.

Third party backend can customize the QueryFragment implementation of this query dsl node via SqlDialect::ExistsSyntax. A customized implementation is expected to provide the same semantics as an ANSI SQL EXIST (subselect) expression.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

subselect: Subselect<T, Bool>

The inner subselect

Trait Implementations

impl<T, QS> AppearsOnTable<QS> for Exists<T>

where Self: Expression, Subselect<T, Bool>: AppearsOnTable<QS>,

impl<T: Clone> Clone for Exists<T>

fn clone(&self) -> Exists<T>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Copy> Copy for Exists<T>

impl<T: Debug> Debug for Exists<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> Expression for Exists<T>

where Subselect<T, Bool>: Expression,

type SqlType = Bool

The type that this expression represents in SQL

impl<T, DB> QueryFragment<DB, AnsiSqlExistsSyntax> for Exists<T>

where DB: Backend + SqlDialect<ExistsSyntax = AnsiSqlExistsSyntax>, T: QueryFragment<DB>,

fn walk_ast<'b>(&'b self, out: AstPass<'_, 'b, DB>) -> QueryResult<()>

Walk over this QueryFragment for all passes.

fn to_sql(&self, out: &mut DB::QueryBuilder, backend: &DB) -> QueryResult<()>

Converts this QueryFragment to its SQL representation.

fn collect_binds<'b>( &'b self, out: &mut DB::BindCollector<'b>, metadata_lookup: &mut DB::MetadataLookup, backend: &'b DB, ) -> QueryResult<()>

Serializes all bind parameters in this query.

fn is_safe_to_cache_prepared(&self, backend: &DB) -> QueryResult<bool>

Is this query safe to store in the prepared statement cache?

fn is_noop(&self, backend: &DB) -> QueryResult<bool>

Does walking this AST have any effect?

impl<T, DB> QueryFragment<DB> for Exists<T>

where DB: Backend, Self: QueryFragment<DB, DB::ExistsSyntax>,

fn walk_ast<'b>(&'b self, pass: AstPass<'_, 'b, DB>) -> QueryResult<()>

Walk over this QueryFragment for all passes.

fn to_sql(&self, out: &mut DB::QueryBuilder, backend: &DB) -> QueryResult<()>

Converts this QueryFragment to its SQL representation.

fn collect_binds<'b>( &'b self, out: &mut DB::BindCollector<'b>, metadata_lookup: &mut DB::MetadataLookup, backend: &'b DB, ) -> QueryResult<()>

Serializes all bind parameters in this query.

fn is_safe_to_cache_prepared(&self, backend: &DB) -> QueryResult<bool>

Is this query safe to store in the prepared statement cache?

fn is_noop(&self, backend: &DB) -> QueryResult<bool>

Does walking this AST have any effect?

impl<T: QueryId> QueryId for Exists<T>

const HAS_STATIC_QUERY_ID: bool

Can the SQL generated by Self be uniquely identified by its type?

type QueryId = Exists<<T as QueryId>::QueryId>

A type which uniquely represents Self in a SQL query.

fn query_id() -> Option<TypeId>

Returns the type id of Self::QueryId if Self::HAS_STATIC_QUERY_ID. Returns None otherwise.

impl<T, QS> SelectableExpression<QS> for Exists<T>

where Self: AppearsOnTable<QS>, Subselect<T, Bool>: SelectableExpression<QS>,

impl<T, GB> ValidGrouping<GB> for Exists<T>

where Subselect<T, Bool>: ValidGrouping<GB>,

type IsAggregate = <Subselect<T, Bool> as ValidGrouping<GB>>::IsAggregate

Is this expression aggregate?