executor: fix float data accuracy (#20440)

server/util.go

@@ -347,14 +347,18 @@ func lengthEncodedIntSize(n uint64) int {
 }
 
 const (
-	expFormatBig   = 1e15
-	expFormatSmall = 1e-15
+	expFormatBig     = 1e15
+	expFormatSmall   = 1e-15
+	defaultMySQLPrec = 5
 )
 
 func appendFormatFloat(in []byte, fVal float64, prec, bitSize int) []byte {
 	absVal := math.Abs(fVal)
 	var out []byte
 	if prec == types.UnspecifiedLength && (absVal >= expFormatBig || (absVal != 0 && absVal < expFormatSmall)) {
+		if bitSize == 32 {
+			prec = defaultMySQLPrec
+		}
 		out = strconv.AppendFloat(in, fVal, 'e', prec, bitSize)
 		valStr := out[len(in):]
 		// remove the '+' from the string for compatibility.
@@ -363,6 +367,20 @@ func appendFormatFloat(in []byte, fVal float64, prec, bitSize int) []byte {
 			plusPosInOut := len(in) + plusPos
 			out = append(out[:plusPosInOut], out[plusPosInOut+1:]...)
 		}
+		// remove extra '0'
+		ePos := bytes.IndexByte(valStr, 'e')
+		pointPos := bytes.IndexByte(valStr, '.')
+		ePosInOut := len(in) + ePos
+		pointPosInOut := len(in) + pointPos
+		validPos := ePosInOut
+		for i := ePosInOut - 1; i >= pointPosInOut; i-- {
+			if out[i] == '0' || out[i] == '.' {
+				validPos = i
+			} else {
+				break
+			}
+		}
+		out = append(out[:validPos], out[ePosInOut:]...)
 	} else {
 		out = strconv.AppendFloat(in, fVal, 'f', prec, bitSize)
 	}

server/util_test.go

@@ -341,6 +341,54 @@ func (s *testUtilSuite) TestAppendFormatFloat(c *C) {
 			-1,
 			64,
 		},
+		{
+			-340282346638528860000000000000000000000,
+			"-3.40282e38",
+			-1,
+			32,
+		},
+		{
+			-34028236,
+			"-34028236.00",
+			2,
+			32,
+		},
+		{
+			-17976921.34,
+			"-17976921.34",
+			2,
+			64,
+		},
+		{
+			-3.402823466e+38,
+			"-3.40282e38",
+			-1,
+			32,
+		},
+		{
+			-1.7976931348623157e308,
+			"-1.7976931348623157e308",
+			-1,
+			64,
+		},
+		{
+			10.0e20,
+			"1e21",
+			-1,
+			32,
+		},
+		{
+			1e20,
+			"1e20",
+			-1,
+			32,
+		},
+		{
+			10.0,
+			"10",
+			-1,
+			32,
+		},
 	}
 	for _, t := range tests {
 		c.Assert(string(appendFormatFloat(nil, t.fVal, t.prec, t.bitSize)), Equals, t.out)