From c663361a10d088e4e351c8f94cb9d260eac0ee41 Mon Sep 17 00:00:00 2001
From: Kenan Yao <cauchy1992@gmail.com>
Date: Wed, 17 Jul 2019 15:51:07 +0800
Subject: [PATCH] *: add `Not` flag for `ExistsSubqueryExpr`

Parser part of the cherry-pick for https://github.com/pingcap/tidb/pull/7842
---
 ast/expressions.go |  2 ++
 parser.go          |  8 +++++++-
 parser.y           |  8 +++++++-
 parser_test.go     | 17 +++++++++++++++++
 4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/ast/expressions.go b/ast/expressions.go
index 6a894682d..61e523c8b 100644
--- a/ast/expressions.go
+++ b/ast/expressions.go
@@ -443,6 +443,8 @@ type ExistsSubqueryExpr struct {
 	exprNode
 	// Sel is the subquery, may be rewritten to other type of expression.
 	Sel ExprNode
+	// Not is true, the expression is "not exists".
+	Not bool
 }
 
 // Format the ExprNode into a Writer.
diff --git a/parser.go b/parser.go
index 06f4463d7..fd3dcd8cd 100644
--- a/parser.go
+++ b/parser.go
@@ -8351,7 +8351,13 @@ yynewstate:
 		}
 	case 263:
 		{
-			parser.yyVAL.expr = &ast.UnaryOperationExpr{Op: opcode.Not, V: yyS[yypt-0].expr}
+			expr, ok := yyS[yypt-0].expr.(*ast.ExistsSubqueryExpr)
+			if ok {
+				expr.Not = true
+				parser.yyVAL.expr = yyS[yypt-0].expr
+			} else {
+				parser.yyVAL.expr = &ast.UnaryOperationExpr{Op: opcode.Not, V: yyS[yypt-0].expr}
+			}
 		}
 	case 264:
 		{
diff --git a/parser.y b/parser.y
index 6e7a08e94..da0e3fd86 100644
--- a/parser.y
+++ b/parser.y
@@ -2568,7 +2568,13 @@ Expression:
 	}
 |	"NOT" Expression %prec not
 	{
-		$$ = &ast.UnaryOperationExpr{Op: opcode.Not, V: $2}
+		expr, ok := $2.(*ast.ExistsSubqueryExpr)
+		if ok {
+			expr.Not = true
+			$$ = $2
+		} else {
+			$$ = &ast.UnaryOperationExpr{Op: opcode.Not, V: $2}
+		}
 	}
 |	BoolPri IsOrNotOp trueKwd %prec is
 	{
diff --git a/parser_test.go b/parser_test.go
index 8fd99b028..8549628a0 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -2704,3 +2704,20 @@ func (s *testParserSuite) TestFieldText(c *C) {
 		c.Assert(traceStmt.Stmt.Text(), Equals, "select a from t")
 	}
 }
+
+func (s *testParserSuite) TestNotExistsSubquery(c *C) {
+	table := []testCase{
+		{`select * from t1 where not exists (select * from t2 where t1.a = t2.a)`, true},
+	}
+
+ 	parser := New()
+	for _, tt := range table {
+		stmt, _, err := parser.Parse(tt.src, "", "")
+		c.Assert(err, IsNil)
+
+ 		sel := stmt[0].(*ast.SelectStmt)
+		exists, ok := sel.Where.(*ast.ExistsSubqueryExpr)
+		c.Assert(ok, IsTrue)
+		c.Assert(exists.Not, Equals, tt.ok)
+	}
+}