expression: fix a bug when datum.kind is not consistent with expression.type (#4269)

expression/expression.go

@@ -177,7 +177,9 @@ func evalExprToReal(expr Expression, row []types.Datum, sc *variable.StatementCo
 		return res, val.IsNull(), errors.Trace(err)
 	}
 	if expr.GetTypeClass() == types.ClassReal {
-		return val.GetFloat64(), false, nil
+		// TODO: fix this to val.GetFloat64() after all built-in functions been rewritten.
+		res, err = val.ToFloat64(sc)
+		return res, false, errors.Trace(err)
 	} else if IsHybridType(expr) {
 		res, err = val.ToFloat64(sc)
 		return res, false, errors.Trace(err)
@@ -200,7 +202,7 @@ func evalExprToDecimal(expr Expression, row []types.Datum, sc *variable.Statemen
 		// we infer the result type of the sql as `mysql.TypeNewDecimal` which is consistent with MySQL,
 		// but what we actually get is store as float64 in Datum.
 		// So if we wrap `CastDecimalAsInt` upon the result, we'll get <nil> when call `arg.EvalDecimal()`.
-		// This will be fixed after all built-in functions be rewrite correctlly.
+		// This will be fixed after all built-in functions be rewrite correctly.
 	} else if IsHybridType(expr) {
 		res, err = val.ToDecimal(sc)
 		return res, false, errors.Trace(err)

expression/integration_test.go

@@ -1525,6 +1525,8 @@ func (s *testIntegrationSuite) TestControlBuiltin(c *C) {
 	result = tk.MustQuery("SELECT 79 + + + CASE -87 WHEN -30 THEN COALESCE(COUNT(*), +COALESCE(+15, -33, -12 ) + +72) WHEN +COALESCE(+AVG(DISTINCT(60)), 21) THEN NULL ELSE NULL END AS col0;")
 	result.Check(testkit.Rows("<nil>"))
 
+	result = tk.MustQuery("SELECT -63 + COALESCE ( - 83, - 61 + - + 72 * - CAST( NULL AS SIGNED ) + + 3 );")
+	result.Check(testkit.Rows("-146"))
 }
 
 func (s *testIntegrationSuite) TestArithmeticBuiltin(c *C) {