Add Table.none

Acts as a "black hole" query, rendering as an empty SQL string and not
executed by the database.

Author: stephencelis

Sources/StructuredQueries/Macros.swift

@@ -10,6 +10,7 @@ import StructuredQueriesCore
   PartialSelectStatement,
   PrimaryKeyedTable,
   names: named(From),
+  // named(all),
   named(columns),
   named(init(_:)),
   named(init(decoder:)),

Sources/StructuredQueriesCore/Internal/Scope.swift

@@ -0,0 +1,5 @@
+enum Scope {
+  case unscoped
+  case `default`
+  case empty
+}

Sources/StructuredQueriesCore/Statements/CompoundSelect.swift

@@ -66,6 +66,8 @@ private struct CompoundSelect<QueryValue>: PartialSelectStatement {
   }
 
   var query: QueryFragment {
-    "\(lhs)\(.newlineOrSpace)\(`operator`.indented())\(.newlineOrSpace)\(rhs)"
+    guard !lhs.isEmpty else { return rhs }
+    guard !rhs.isEmpty else { return lhs }
+    return "\(lhs)\(.newlineOrSpace)\(`operator`.indented())\(.newlineOrSpace)\(rhs)"
   }
 }

Sources/StructuredQueriesCore/Statements/Delete.swift

@@ -38,6 +38,7 @@ extension PrimaryKeyedTable {
 public struct Delete<From: Table, Returning> {
   var `where`: [QueryFragment] = []
   var returning: [QueryFragment] = []
+  var isEmpty = false
 
   /// Adds a condition to a delete statement.
   ///
@@ -130,6 +131,16 @@ public struct Delete<From: Table, Returning> {
       returning: returning
     )
   }
+
+  public var unscoped: Delete<From, ()> {
+    From.unscoped.delete()
+  }
+
+  public var none: Self {
+    var delete = self
+    delete.isEmpty = true
+    return delete
+  }
 }
 
 /// A convenience type alias for a non-`RETURNING ``Delete``.
@@ -139,6 +150,7 @@ extension Delete: Statement {
   public typealias QueryValue = Returning
 
   public var query: QueryFragment {
+    guard !isEmpty else { return "" }
     var query: QueryFragment = "DELETE FROM "
     if let schemaName = From.schemaName {
       query.append("\(quote: schemaName).")

Sources/StructuredQueriesCore/Statements/Select.swift

@@ -297,6 +297,7 @@ extension Table {
 }
 
 public struct _SelectClauses: Sendable {
+  var isEmpty = false
   var distinct = false
   var columns: [any QueryExpression] = []
   var joins: [_JoinClause] = []
@@ -320,6 +321,11 @@ public struct Select<Columns, From: Table, Joins> {
   // NB: A parameter pack compiler crash forces us to heap-allocate this storage.
   @CopyOnWrite var clauses = _SelectClauses()
 
+  fileprivate var isEmpty: Bool {
+    get { clauses.isEmpty }
+    set { clauses.isEmpty = newValue }
+    _modify { yield &clauses.isEmpty }
+  }
   fileprivate var distinct: Bool {
     get { clauses.distinct }
     set { clauses.distinct = newValue }
@@ -362,6 +368,7 @@ public struct Select<Columns, From: Table, Joins> {
   }
 
   fileprivate init(
+    isEmpty: Bool,
     distinct: Bool,
     columns: [any QueryExpression],
     joins: [_JoinClause],
@@ -371,6 +378,7 @@ public struct Select<Columns, From: Table, Joins> {
     order: [QueryFragment],
     limit: _LimitClause?
   ) {
+    self.isEmpty = isEmpty
     self.columns = columns
     self.distinct = distinct
     self.joins = joins
@@ -387,7 +395,8 @@ public struct Select<Columns, From: Table, Joins> {
 }
 
 extension Select {
-  init(where: [QueryFragment] = []) {
+  init(isEmpty: Bool = false, where: [QueryFragment] = []) {
+    self.isEmpty = isEmpty
     self.where = `where`
   }
 
@@ -558,6 +567,7 @@ extension Select {
     Joins == (repeat each J)
   {
     Select<(repeat each C1, repeat (each C2).QueryValue), From, (repeat each J)>(
+      isEmpty: isEmpty,
       distinct: distinct,
       columns: columns + Array(repeat each selection((From.columns, repeat (each J).columns))),
       joins: joins,
@@ -612,6 +622,7 @@ extension Select {
       )
     )
     return Select<(repeat each C1, repeat each C2), From, (repeat each J1, F, repeat each J2)>(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -651,6 +662,7 @@ extension Select {
       )
     )
     return Select<(repeat each C1, repeat each C2), From, (repeat each J, F)>(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -686,6 +698,7 @@ extension Select {
       )
     )
     return Select<QueryValue, From, (F, repeat each J)>(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -738,6 +751,7 @@ extension Select {
       From,
       (repeat each J1, F._Optionalized, repeat (each J2)._Optionalized)
     >(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -785,6 +799,7 @@ extension Select {
       From,
       (repeat each J, F._Optionalized)
     >(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -822,6 +837,7 @@ extension Select {
       )
     )
     return Select<QueryValue, From, (F._Optionalized, repeat (each J)._Optionalized)>(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -874,6 +890,7 @@ extension Select {
       From._Optionalized,
       (repeat (each J1)._Optionalized, F, repeat each J2)
     >(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -921,6 +938,7 @@ extension Select {
       From._Optionalized,
       (repeat (each J)._Optionalized, F)
     >(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -958,6 +976,7 @@ extension Select {
       )
     )
     return Select<QueryValue, From._Optionalized, (F, repeat each J)>(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -1010,6 +1029,7 @@ extension Select {
       From._Optionalized,
       (repeat (each J1)._Optionalized, F._Optionalized, repeat (each J2)._Optionalized)
     >(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -1057,6 +1077,7 @@ extension Select {
       From._Optionalized,
       (repeat (each J)._Optionalized, F._Optionalized)
     >(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -1094,6 +1115,7 @@ extension Select {
       )
     )
     return Select<QueryValue, From._Optionalized, (F._Optionalized, repeat (each J)._Optionalized)>(
+      isEmpty: isEmpty || other.isEmpty,
       distinct: distinct || other.distinct,
       columns: columns + other.columns,
       joins: joins + [join] + other.joins,
@@ -1348,6 +1370,7 @@ extension Select {
       SQLQueryExpression(iterator.next()!.queryFragment)
     }
     return Select<(repeat (each C2).QueryValue), From, Joins>(
+      isEmpty: isEmpty,
       distinct: distinct,
       columns: Array(repeat each transform(repeat { _ in next() }((each C1).self))),
       joins: joins,
@@ -1358,6 +1381,20 @@ extension Select {
       limit: limit
     )
   }
+
+  public var unscoped: Where<From> {
+    From.unscoped
+  }
+
+  public var all: Self {
+    self
+  }
+
+  public var none: Self {
+    var select = self
+    select.isEmpty = true
+    return select
+  }
 }
 
 /// Combines two select statements of the same table type together.
@@ -1387,6 +1424,7 @@ public func + <
   return Select<
     (repeat each C1, repeat each C2), From, (repeat each J1, repeat each J2)
   >(
+    isEmpty: lhs.isEmpty || rhs.isEmpty,
     distinct: lhs.distinct || rhs.distinct,
     columns: lhs.columns + rhs.columns,
     joins: lhs.joins + rhs.joins,
@@ -1406,6 +1444,7 @@ extension Select: SelectStatement {
   }
 
   public var query: QueryFragment {
+    guard !isEmpty else { return "" }
     var query: QueryFragment = "SELECT"
     let columns =
       columns.isEmpty

Sources/StructuredQueriesCore/Statements/Update.swift

@@ -95,6 +95,7 @@ public struct Update<From: Table, Returning> {
   var updates: Updates<From>
   var `where`: [QueryFragment] = []
   var returning: [QueryFragment] = []
+  var isEmpty = false
 
   /// Adds a condition to an update statement.
   ///
@@ -186,6 +187,16 @@ public struct Update<From: Table, Returning> {
       returning: returning
     )
   }
+
+  public var unscoped: Delete<From, ()> {
+    From.unscoped.delete()
+  }
+
+  public var none: Self {
+    var delete = self
+    delete.isEmpty = true
+    return delete
+  }
 }
 
 /// A convenience type alias for a non-`RETURNING ``Update``.
@@ -195,7 +206,7 @@ extension Update: Statement {
   public typealias QueryValue = Returning
 
   public var query: QueryFragment {
-    guard !updates.isEmpty
+    guard !isEmpty, !updates.isEmpty
     else { return "" }
 
     var query: QueryFragment = "UPDATE "

Sources/StructuredQueriesCore/Statements/Where.swift

@@ -64,7 +64,7 @@ public struct Where<From: Table> {
   }
 
   var predicates: [QueryFragment] = []
-  var unscoped = false
+  var scope = Scope.default
 
   #if compiler(>=6.1)
     public static subscript(dynamicMember keyPath: KeyPath<From.Type, Self>) -> Self {
@@ -94,12 +94,20 @@ extension Where: SelectStatement {
   public typealias QueryValue = ()
 
   public func asSelect() -> SelectOf<From> {
-    (unscoped ? Select() : Select(clauses: From.all._selectClauses))
-      .and(self)
+    let select: SelectOf<From>
+    switch scope {
+    case .default:
+      select = Select(clauses: From.all._selectClauses)
+    case .empty:
+      select = Select(isEmpty: true, where: predicates)
+    case .unscoped:
+      select = Select()
+    }
+    return select.and(self)
   }
 
   public var _selectClauses: _SelectClauses {
-    _SelectClauses(where: predicates)
+    _SelectClauses(isEmpty: scope == .empty, where: predicates)
   }
 
   /// A select statement for a column of the filtered table.
@@ -470,7 +478,10 @@ extension Where: SelectStatement {
 
   /// A delete statement for the filtered table.
   public func delete() -> DeleteOf<From> {
-    Delete(where: unscoped ? predicates : From.all._selectClauses.where + predicates)
+    Delete(
+      where: scope == .unscoped ? predicates : From.all._selectClauses.where + predicates,
+      isEmpty: scope == .empty
+    )
   }
 
   /// An update statement for the filtered table.
@@ -486,7 +497,8 @@ extension Where: SelectStatement {
     Update(
       conflictResolution: conflictResolution,
       updates: Updates(updates),
-      where: unscoped ? predicates : From.all._selectClauses.where + predicates
+      where: scope == .unscoped ? predicates : From.all._selectClauses.where + predicates,
+      isEmpty: scope == .empty
     )
   }
 

Sources/StructuredQueriesCore/Table.swift

@@ -49,12 +49,6 @@ public protocol Table: QueryRepresentable where TableColumns.QueryValue == Self
   static var all: DefaultScope { get }
 }
 
-extension Table where DefaultScope == Where<Self> {
-  public static var all: DefaultScope {
-    Where()
-  }
-}
-
 extension Table {
   /// A select statement on the table with no constraints.
   ///
@@ -86,7 +80,11 @@ extension Table {
   /// // SELECT "reminders"."id" FROM "reminders"
   /// ```
   public static var unscoped: Where<Self> {
-    Where(unscoped: true)
+    Where(scope: .unscoped)
+  }
+
+  public static var none: Where<Self> {
+    Where(scope: .empty)
   }
 
   public static var tableAlias: String? {
@@ -112,3 +110,9 @@ extension Table {
     columns[keyPath: keyPath]
   }
 }
+
+extension Table where DefaultScope == Where<Self> {
+  public static var all: DefaultScope {
+    Where()
+  }
+}