Support \N shortcut for null

executor/executor_test.go

@@ -217,6 +217,58 @@ func (s *testSuite) TestSelectWithoutFrom(c *C) {
 	r.Check(testkit.Rows("string"))
 }
 
+func (s *testSuite) TestSelectBackslashN(c *C) {
+	defer func() {
+		s.cleanEnv(c)
+		testleak.AfterTest(c)()
+	}()
+	tk := testkit.NewTestKit(c, s.store)
+
+	sql := `select \N;`
+	r := tk.MustQuery(sql)
+	r.Check(testkit.Rows("<nil>"))
+	rs, err := tk.Exec(sql)
+	c.Check(err, IsNil)
+	fields, err := rs.Fields()
+	c.Check(err, IsNil)
+	c.Check(len(fields), Equals, 1)
+	c.Check(fields[0].Column.Name.O, Equals, "NULL")
+
+	sql = `select "\N";`
+	r = tk.MustQuery(sql)
+	r.Check(testkit.Rows("N"))
+	rs, err = tk.Exec(sql)
+	c.Check(err, IsNil)
+	fields, err = rs.Fields()
+	c.Check(err, IsNil)
+	c.Check(len(fields), Equals, 1)
+	c.Check(fields[0].Column.Name.O, Equals, `"\N"`)
+
+	tk.MustExec("use test;")
+	tk.MustExec("create table test (`\\N` int);")
+	tk.MustExec("insert into test values (1);")
+	tk.CheckExecResult(1, 0)
+	sql = "select * from test;"
+	r = tk.MustQuery(sql)
+	r.Check(testkit.Rows("1"))
+	rs, err = tk.Exec(sql)
+	c.Check(err, IsNil)
+	fields, err = rs.Fields()
+	c.Check(err, IsNil)
+	c.Check(len(fields), Equals, 1)
+	c.Check(fields[0].Column.Name.O, Equals, `\N`)
+
+	sql = "select \\N from test;"
+	r = tk.MustQuery(sql)
+	r.Check(testkit.Rows("<nil>"))
+	rs, err = tk.Exec(sql)
+	c.Check(err, IsNil)
+	fields, err = rs.Fields()
+	c.Check(err, IsNil)
+	c.Check(len(fields), Equals, 1)
+	c.Check(fields[0].Column.Name.O, Equals, `NULL`)
+}
+
 func (s *testSuite) TestSelectLimit(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	defer func() {

parser/lexer_test.go

@@ -120,6 +120,7 @@ func (s *testLexerSuite) TestLiteral(c *C) {
 		{".1_t_1_x", int('.')},
 		{"N'some text'", underscoreCS},
 		{"n'some text'", underscoreCS},
+		{"\\N", null},
 	}
 	runTest(c, table)
 }

parser/misc.go

@@ -119,6 +119,7 @@ func init() {
 	initTokenString("<>", neqSynonym)
 	initTokenString("<<", lsh)
 	initTokenString(">>", rsh)
+	initTokenString("\\N", null)
 
 	initTokenFunc("@", startWithAt)
 	initTokenFunc("/", startWithSlash)

plan/logical_plan_builder.go

@@ -426,8 +426,14 @@ func (b *planBuilder) buildProjection(p LogicalPlan, fields []*ast.SelectField,
 				if _, ok := innerExpr.(*ast.ValueExpr); ok && innerExpr.Text() != "" {
 					colName = model.NewCIStr(innerExpr.Text())
 				} else {
+					//Change column name \N to NUll, just when original sql contains \N column
+					fieldText := field.Text()
+					if fieldText == "\\N" {
+						fieldText = "NULL"
+					}
+
 					// Remove special comment code for field part, see issue #3739 for detail.
-					colName = model.NewCIStr(parser.SpecFieldPattern.ReplaceAllStringFunc(field.Text(), parser.TrimComment))
+					colName = model.NewCIStr(parser.SpecFieldPattern.ReplaceAllStringFunc(fieldText, parser.TrimComment))
 				}
 			}
 		}