Support DISTINCT/ALL for aggregate functions

parser.go

@@ -2373,6 +2373,16 @@ func (p *Parser) parsePrefix() (sqlast.Node, error) {
 
 func (p *Parser) parseFunction(name *sqlast.ObjectName) (sqlast.Node, error) {
 	p.expectToken(sqltoken.LParen)
+
+	var filter *sqlast.Ident
+	if ok, _, _ := p.parseKeyword("DISTINCT"); ok {
+		p.prevToken()
+		filter, _ = p.parseIdentifier()
+	} else if ok, _, _ := p.parseKeyword("ALL"); ok {
+		p.prevToken()
+		filter, _ = p.parseIdentifier()
+	}
+
 	args, err := p.parseOptionalArgs()
 	if err != nil {
 		return nil, errors.Errorf("parseOptionalArgs failed: %w", err)
@@ -2434,6 +2444,7 @@ func (p *Parser) parseFunction(name *sqlast.ObjectName) (sqlast.Node, error) {
 		Args:       args,
 		Over:       over,
 		ArgsRParen: r.To,
+		Filter:     filter,
 	}, nil
 }
 

parser_test.go

@@ -908,6 +908,56 @@ FROM user WHERE id BETWEEN 1 AND 2`,
 					},
 				},
 			},
+			{
+				name: "count distinct",
+				in:   "SELECT COUNT(DISTINCT email) FROM user",
+				out: &sqlast.QueryStmt{
+					Body: &sqlast.SQLSelect{
+						Select: sqltoken.NewPos(1, 1),
+						Projection: []sqlast.SQLSelectItem{
+							&sqlast.UnnamedSelectItem{
+								Node: &sqlast.Function{
+									Name: &sqlast.ObjectName{
+										Idents: []*sqlast.Ident{
+											{
+												Value: "COUNT",
+												From:  sqltoken.NewPos(1, 8),
+												To:    sqltoken.NewPos(1, 13),
+											},
+										},
+									},
+									Args: []sqlast.Node{
+										&sqlast.Ident{
+											Value: "email",
+											From:  sqltoken.NewPos(1, 23),
+											To:    sqltoken.NewPos(1, 28),
+										},
+									},
+									Filter: &sqlast.Ident{
+										Value: "DISTINCT",
+										From:  sqltoken.NewPos(1, 14),
+										To:    sqltoken.NewPos(1, 22),
+									},
+									ArgsRParen: sqltoken.NewPos(1, 29),
+								},
+							},
+						},
+						FromClause: []sqlast.TableReference{
+							&sqlast.Table{
+								Name: &sqlast.ObjectName{
+									Idents: []*sqlast.Ident{
+										{
+											Value: "user",
+											From:  sqltoken.NewPos(1, 35),
+											To:    sqltoken.NewPos(1, 39),
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
 		}
 
 		for _, c := range cases {

sqlast/ast.go

@@ -405,6 +405,7 @@ func (s *UnaryExpr) WriteTo(w io.Writer) (int64, error) {
 type Function struct {
 	Name       *ObjectName // Function Name
 	Args       []Node
+	Filter     *Ident
 	ArgsRParen sqltoken.Pos // function args RParen position
 	Over       *WindowSpec
 	OverRparen sqltoken.Pos // Over RParen position (if Over is not nil)