expression: fix cast json to decimal bug. (#8030)

executor/executor_test.go

@@ -1332,6 +1332,21 @@ func (s *testSuite) TestJSON(c *C) {
 	// check CAST AS JSON.
 	result = tk.MustQuery(`select CAST('3' AS JSON), CAST('{}' AS JSON), CAST(null AS JSON)`)
 	result.Check(testkit.Rows(`3 {} <nil>`))
+
+	// Check cast json to decimal.
+	tk.MustExec("drop table if exists test_json")
+	tk.MustExec("create table test_json ( a decimal(60,2) as (JSON_EXTRACT(b,'$.c')), b json );")
+	tk.MustExec(`insert into test_json (b) values
+		('{"c": "1267.1"}'),
+		('{"c": "1267.01"}'),
+		('{"c": "1267.1234"}'),
+		('{"c": "1267.3456"}'),
+		('{"c": "1234567890123456789012345678901234567890123456789012345"}'),
+		('{"c": "1234567890123456789012345678901234567890123456789012345.12345"}');`)
+
+	tk.MustQuery("select a from test_json;").Check(testkit.Rows("1267.10", "1267.01", "1267.12",
+		"1267.35", "1234567890123456789012345678901234567890123456789012345.00",
+		"1234567890123456789012345678901234567890123456789012345.12"))
 }
 
 func (s *testSuite) TestMultiUpdate(c *C) {

expression/builtin_cast.go

@@ -1541,11 +1541,11 @@ func (b *builtinCastJSONAsDecimalSig) evalDecimal(row chunk.Row) (res *types.MyD
 		return res, isNull, errors.Trace(err)
 	}
 	sc := b.ctx.GetSessionVars().StmtCtx
-	f64, err := types.ConvertJSONToFloat(sc, val)
-	if err == nil {
-		res = new(types.MyDecimal)
-		err = res.FromFloat64(f64)
+	res, err = types.ConvertJSONToDecimal(sc, val)
+	if err != nil {
+		return res, false, errors.Trace(err)
 	}
+	res, err = types.ProduceDecWithSpecifiedTp(res, b.tp, sc)
 	return res, false, errors.Trace(err)
 }
 

expression/builtin_cast_test.go

@@ -1082,6 +1082,48 @@ func (s *testEvaluatorSuite) TestCastFuncSig(c *C) {
 	c.Assert(iRes, Equals, int64(0))
 }
 
+func (s *testEvaluatorSuite) TestCastJSONAsDecimalSig(c *C) {
+	ctx, sc := s.ctx, s.ctx.GetSessionVars().StmtCtx
+	originIgnoreTruncate := sc.IgnoreTruncate
+	sc.IgnoreTruncate = true
+	defer func() {
+		sc.IgnoreTruncate = originIgnoreTruncate
+	}()
+
+	col := &Column{RetType: types.NewFieldType(mysql.TypeJSON), Index: 0}
+	decFunc := newBaseBuiltinCastFunc(newBaseBuiltinFunc(ctx, []Expression{col}), false)
+	decFunc.tp = types.NewFieldType(mysql.TypeNewDecimal)
+	decFunc.tp.Flen = 60
+	decFunc.tp.Decimal = 2
+	sig := &builtinCastJSONAsDecimalSig{decFunc}
+
+	var tests = []struct {
+		In  string
+		Out *types.MyDecimal
+	}{
+		{`{}`, types.NewDecFromStringForTest("0")},
+		{`[]`, types.NewDecFromStringForTest("0")},
+		{`3`, types.NewDecFromStringForTest("3")},
+		{`-3`, types.NewDecFromStringForTest("-3")},
+		{`4.5`, types.NewDecFromStringForTest("4.5")},
+		{`"1234"`, types.NewDecFromStringForTest("1234")},
+		// test truncate
+		{`"1234.1234"`, types.NewDecFromStringForTest("1234.12")},
+		{`"1234.4567"`, types.NewDecFromStringForTest("1234.46")},
+		// test big decimal
+		{`"1234567890123456789012345678901234567890123456789012345"`, types.NewDecFromStringForTest("1234567890123456789012345678901234567890123456789012345")},
+	}
+	for _, tt := range tests {
+		j, err := json.ParseBinaryFromString(tt.In)
+		c.Assert(err, IsNil)
+		row := chunk.MutRowFromDatums([]types.Datum{types.NewDatum(j)})
+		res, isNull, err := sig.evalDecimal(row.ToRow())
+		c.Assert(isNull, Equals, false)
+		c.Assert(err, IsNil)
+		c.Assert(res.Compare(tt.Out), Equals, 0)
+	}
+}
+
 // TestWrapWithCastAsTypesClasses tests WrapWithCastAsInt/Real/String/Decimal.
 func (s *testEvaluatorSuite) TestWrapWithCastAsTypesClasses(c *C) {
 	ctx := s.ctx

types/convert.go

@@ -378,6 +378,21 @@ func ConvertJSONToFloat(sc *stmtctx.StatementContext, j json.BinaryJSON) (float6
 	return 0, errors.New("Unknown type code in JSON")
 }
 
+// ConvertJSONToDecimal casts JSON into decimal.
+func ConvertJSONToDecimal(sc *stmtctx.StatementContext, j json.BinaryJSON) (*MyDecimal, error) {
+	res := new(MyDecimal)
+	if j.TypeCode != json.TypeCodeString {
+		f64, err := ConvertJSONToFloat(sc, j)
+		if err != nil {
+			return res, errors.Trace(err)
+		}
+		err = res.FromFloat64(f64)
+		return res, errors.Trace(err)
+	}
+	err := sc.HandleTruncate(res.FromString([]byte(j.GetString())))
+	return res, errors.Trace(err)
+}
+
 // getValidFloatPrefix gets prefix of string which can be successfully parsed as float.
 func getValidFloatPrefix(sc *stmtctx.StatementContext, s string) (valid string, err error) {
 	var (

types/convert_test.go

@@ -804,6 +804,27 @@ func (s *testTypeConvertSuite) TestConvertJSONToFloat(c *C) {
 	}
 }
 
+func (s *testTypeConvertSuite) TestConvertJSONToDecimal(c *C) {
+	var tests = []struct {
+		In  string
+		Out *MyDecimal
+	}{
+		{`{}`, NewDecFromStringForTest("0")},
+		{`[]`, NewDecFromStringForTest("0")},
+		{`3`, NewDecFromStringForTest("3")},
+		{`-3`, NewDecFromStringForTest("-3")},
+		{`4.5`, NewDecFromStringForTest("4.5")},
+		{`"1234"`, NewDecFromStringForTest("1234")},
+		{`"1234567890123456789012345678901234567890123456789012345"`, NewDecFromStringForTest("1234567890123456789012345678901234567890123456789012345")},
+	}
+	for _, tt := range tests {
+		j, err := json.ParseBinaryFromString(tt.In)
+		c.Assert(err, IsNil)
+		casted, _ := ConvertJSONToDecimal(new(stmtctx.StatementContext), j)
+		c.Assert(casted.Compare(tt.Out), Equals, 0)
+	}
+}
+
 func (s *testTypeConvertSuite) TestNumberToDuration(c *C) {
 	var testCases = []struct {
 		number int64