expression: Support push function replace down to TiFlash

expression/expr_to_pb_test.go

@@ -729,6 +729,11 @@ func (s *testEvaluatorSuite) TestExprPushDownToFlash(c *C) {
 	c.Assert(err, IsNil)
 	exprs = append(exprs, function)
 
+	// Replace
+	function, err = NewFunction(mock.NewContext(), ast.Replace, types.NewFieldType(mysql.TypeString), stringColumn, stringColumn, stringColumn)
+	c.Assert(err, IsNil)
+	exprs = append(exprs, function)
+
 	function, err = NewFunction(mock.NewContext(), ast.Round, types.NewFieldType(mysql.TypeDouble), realColumn)
 	c.Assert(err, IsNil)
 	exprs = append(exprs, function)

expression/expression.go

@@ -1036,6 +1036,11 @@ func scalarExprSupportedByFlash(function *ScalarFunction) bool {
 		case tipb.ScalarFuncSig_ExtractDatetime:
 			return true
 		}
+	case ast.Replace:
+		switch function.Function.PbCode() {
+		case tipb.ScalarFuncSig_Replace:
+			return true
+		}
 	}
 	return false
 }