Support window declarations on select statements

sqlparser/lib/src/analysis/steps/reference_finder.dart

@@ -42,6 +42,10 @@ class ReferenceFinder extends RecursiveVisitor<void> {
       e.scope = forked;
     }
 
+    for (var windowDecl in e.windowDeclarations) {
+      e.scope.register(windowDecl.name, windowDecl);
+    }
+
     visitChildren(e);
   }
 

sqlparser/lib/src/analysis/steps/reference_resolver.dart

@@ -62,4 +62,14 @@ class ReferenceResolver extends RecursiveVisitor<void> {
 
     visitChildren(e);
   }
+
+  @override
+  void visitAggregateExpression(AggregateExpression e) {
+    if (e.windowName != null) {
+      final resolved = e.scope.resolve<NamedWindowDeclaration>(e.windowName);
+      e.resolved = resolved;
+    }
+
+    visitChildren(e);
+  }
 }

sqlparser/lib/src/ast/expressions/aggregate.dart

@@ -1,6 +1,7 @@
 part of '../ast.dart';
 
-class AggregateExpression extends Expression implements Invocation {
+class AggregateExpression extends Expression
+    implements Invocation, ReferenceOwner {
   final IdentifierToken function;
 
   @override
@@ -9,13 +10,37 @@ class AggregateExpression extends Expression implements Invocation {
   @override
   final FunctionParameters parameters;
   final Expression filter;
-  final WindowDefinition over; // todo support window references
+
+  @override
+  Referencable resolved;
+  WindowDefinition get over {
+    if (windowDefinition != null) return windowDefinition;
+    return (resolved as NamedWindowDeclaration)?.definition;
+  }
+
+  /// The window definition as declared in the `OVER` clause in sql. If this
+  /// aggregate expression didn't declare a window (e.g. it instead uses a
+  /// window via a name declared in the surrounding `SELECT` statement), we're
+  /// this field will be null. Either [windowDefinition] or [windowName] are
+  /// null. The resolved [WindowDefinition] is available in [over] in either
+  /// case.
+  final WindowDefinition windowDefinition;
+
+  /// An aggregate expression can be written as `OVER <window-name>` instead of
+  /// declaring its own [windowDefinition]. Either [windowDefinition] or
+  /// [windowName] are null. The resolved [WindowDefinition] is available in
+  /// [over] in either case.
+  final String windowName;
 
   AggregateExpression(
       {@required this.function,
       @required this.parameters,
       this.filter,
-      @required this.over});
+      this.windowDefinition,
+      this.windowName}) {
+    // either window definition or name must be null
+    assert((windowDefinition == null) != (windowName == null));
+  }
 
   @override
   T accept<T>(AstVisitor<T> visitor) => visitor.visitAggregateExpression(this);
@@ -26,16 +51,28 @@ class AggregateExpression extends Expression implements Invocation {
       if (parameters is ExprFunctionParameters)
         ...(parameters as ExprFunctionParameters).parameters,
       if (filter != null) filter,
-      over,
+      if (windowDefinition != null) windowDefinition,
     ];
   }
 
   @override
   bool contentEquals(AggregateExpression other) {
-    return other.name == name;
+    return other.name == name &&
+        other.windowDefinition == windowDefinition &&
+        other.windowName == windowName;
   }
 }
 
+/// A window declaration that appears in a `SELECT` statement like
+/// `WINDOW <name> AS <window-defn>`. It can be referenced from an
+/// [AggregateExpression] if it uses the same name.
+class NamedWindowDeclaration with Referencable {
+  final String name;
+  final WindowDefinition definition;
+
+  NamedWindowDeclaration(this.name, this.definition);
+}
+
 class WindowDefinition extends AstNode {
   final String baseWindowName;
   final List<Expression> partitionBy;

sqlparser/lib/src/ast/statements/select.dart

@@ -7,6 +7,7 @@ class SelectStatement extends Statement with CrudStatement, ResultSet {
 
   final Expression where;
   final GroupBy groupBy;
+  final List<NamedWindowDeclaration> windowDeclarations;
 
   final OrderBy orderBy;
   final Limit limit;
@@ -22,6 +23,7 @@ class SelectStatement extends Statement with CrudStatement, ResultSet {
       this.from,
       this.where,
       this.groupBy,
+      this.windowDeclarations = const [],
       this.orderBy,
       this.limit});
 
@@ -37,6 +39,7 @@ class SelectStatement extends Statement with CrudStatement, ResultSet {
       if (from != null) ...from,
       if (where != null) where,
       if (groupBy != null) groupBy,
+      for (var windowDecl in windowDeclarations) windowDecl.definition,
       if (limit != null) limit,
       if (orderBy != null) orderBy,
     ];

sqlparser/lib/src/reader/parser/crud.dart

@@ -22,6 +22,7 @@ mixin CrudParser on ParserBase {
 
     final where = _where();
     final groupBy = _groupBy();
+    final windowDecls = _windowDeclarations();
     final orderBy = _orderBy();
     final limit = _limit();
 
@@ -31,6 +32,7 @@ mixin CrudParser on ParserBase {
       from: from,
       where: where,
       groupBy: groupBy,
+      windowDeclarations: windowDecls,
       orderBy: orderBy,
       limit: limit,
     )..setSpan(selectToken, _previous);
@@ -253,8 +255,23 @@ mixin CrudParser on ParserBase {
     return null;
   }
 
+  List<NamedWindowDeclaration> _windowDeclarations() {
+    final declarations = <NamedWindowDeclaration>[];
+    if (_matchOne(TokenType.window)) {
+      do {
+        final name = _consumeIdentifier('Expected a name for the window');
+        _consume(TokenType.as,
+            'Expected AS between the window name and its definition');
+        final window = _windowDefinition();
+
+        declarations.add(NamedWindowDeclaration(name.identifier, window));
+      } while (_matchOne(TokenType.comma));
+    }
+    return declarations;
+  }
+
   OrderBy _orderBy() {
-    if (_match(const [TokenType.order])) {
+    if (_matchOne(TokenType.order)) {
       _consume(TokenType.by, 'Expected "BY" after "ORDER" token');
       final terms = <OrderingTerm>[];
       do {

sqlparser/lib/src/reader/parser/expressions.dart

@@ -373,10 +373,22 @@ mixin ExpressionParser on ParserBase {
     }
 
     _consume(TokenType.over, 'Expected OVER to begin window clause');
-    final window = _windowDefinition();
+
+    String windowName;
+    WindowDefinition window;
+
+    if (_matchOne(TokenType.identifier)) {
+      windowName = (_previous as IdentifierToken).identifier;
+    } else {
+      window = _windowDefinition();
+    }
 
     return AggregateExpression(
-        function: name, parameters: params, filter: filter, over: window)
-      ..setSpan(name, _previous);
+      function: name,
+      parameters: params,
+      filter: filter,
+      windowDefinition: window,
+      windowName: windowName,
+    )..setSpan(name, _previous);
   }
 }

sqlparser/lib/src/reader/tokenizer/token.dart

@@ -88,6 +88,7 @@ enum TokenType {
   $else,
   end,
 
+  window,
   filter,
   over,
   partition,
@@ -222,6 +223,7 @@ const Map<String, TokenType> keywords = {
   'EXCLUDE': TokenType.exclude,
   'OTHERS': TokenType.others,
   'TIES': TokenType.ties,
+  'WINDOW': TokenType.window,
 };
 
 class Token {

sqlparser/test/analysis/reference_resolver_test.dart

@@ -78,4 +78,30 @@ void main() {
 
     expect(context.errors, isEmpty);
   });
+
+  test('resolves window declarations', () {
+    final engine = SqlEngine()..registerTable(demoTable);
+
+    final context = engine.analyze('''
+SELECT current_row() OVER wnd FROM demo
+  WINDOW wnd AS (PARTITION BY content GROUPS CURRENT ROW EXCLUDE TIES)
+    ''');
+
+    final column = (context.root as SelectStatement).resolvedColumns.single
+        as ExpressionColumn;
+
+    final over = (column.expression as AggregateExpression).over;
+
+    enforceEqual(
+      over,
+      WindowDefinition(
+        partitionBy: [Reference(columnName: 'content')],
+        frameSpec: FrameSpec(
+          type: FrameType.groups,
+          start: const FrameBoundary.currentRow(),
+          excludeMode: ExcludeMode.ties,
+        ),
+      ),
+    );
+  });
 }

sqlparser/test/parser/partition_test.dart

@@ -10,7 +10,7 @@ final Map<String, Expression> _testCases = {
   'row_number() OVER (ORDER BY y)': AggregateExpression(
     function: identifier('row_number'),
     parameters: ExprFunctionParameters(),
-    over: WindowDefinition(
+    windowDefinition: WindowDefinition(
       frameSpec: FrameSpec(),
       orderBy: OrderBy(terms: [
         OrderingTerm(expression: Reference(columnName: 'y')),
@@ -24,7 +24,7 @@ final Map<String, Expression> _testCases = {
     function: identifier('row_number'),
     parameters: const StarFunctionParameter(),
     filter: NumericLiteral(1, token(TokenType.numberLiteral)),
-    over: WindowDefinition(
+    windowDefinition: WindowDefinition(
       baseWindowName: 'base_name',
       partitionBy: [
         Reference(columnName: 'a'),
@@ -44,7 +44,7 @@ final Map<String, Expression> _testCases = {
       AggregateExpression(
     function: identifier('row_number'),
     parameters: ExprFunctionParameters(),
-    over: WindowDefinition(
+    windowDefinition: WindowDefinition(
       frameSpec: FrameSpec(
         type: FrameType.range,
         start: const FrameBoundary.currentRow(),