expression: push down expr json_length to tiflash (#17588)

expression/expr_to_pb_test.go

@@ -601,6 +601,25 @@ func (s *testEvaluatorSuite) TestOtherFunc2Pb(c *C) {
 	}
 }
 
+func (s *testEvaluatorSuite) TestExprPushDownToFlash(c *C) {
+	sc := new(stmtctx.StatementContext)
+	client := new(mock.Client)
+	dg := new(dataGen4Expr2PbTest)
+	exprs := make([]Expression, 0)
+	function, err := NewFunction(mock.NewContext(), ast.JSONLength, types.NewFieldType(mysql.TypeLonglong), dg.genColumn(mysql.TypeJSON, 1))
+	c.Assert(err, IsNil)
+	exprs = append(exprs, function)
+	canPush := CanExprsPushDown(sc, exprs, client, kv.TiFlash)
+	c.Assert(canPush, Equals, true)
+
+	function, err = NewFunction(mock.NewContext(), ast.JSONDepth, types.NewFieldType(mysql.TypeLonglong), dg.genColumn(mysql.TypeJSON, 2))
+	c.Assert(err, IsNil)
+	exprs = append(exprs, function)
+	pushed, remained := PushDownExprs(sc, exprs, client, kv.TiFlash)
+	c.Assert(len(pushed), Equals, 1)
+	c.Assert(len(remained), Equals, 1)
+}
+
 func (s *testEvaluatorSuite) TestExprOnlyPushDownToFlash(c *C) {
 	sc := new(stmtctx.StatementContext)
 	client := new(mock.Client)

expression/expression.go

@@ -1059,7 +1059,7 @@ func canScalarFuncPushDown(scalarFunc *ScalarFunction, pc PbConverter, storeType
 }
 
 func canExprPushDown(expr Expression, pc PbConverter, storeType kv.StoreType) bool {
-	if storeType == kv.TiFlash && (expr.GetType().Tp == mysql.TypeDuration || expr.GetType().Tp == mysql.TypeJSON || collate.NewCollationEnabled()) {
+	if storeType == kv.TiFlash && (expr.GetType().Tp == mysql.TypeDuration || collate.NewCollationEnabled()) {
 		return false
 	}
 	switch x := expr.(type) {
@@ -1119,7 +1119,8 @@ func scalarExprSupportedByFlash(function *ScalarFunction) bool {
 		ast.LT, ast.GT, ast.Ifnull, ast.IsNull, ast.Or,
 		ast.In, ast.Mod, ast.And, ast.LogicOr, ast.LogicAnd,
 		ast.Like, ast.UnaryNot, ast.Case, ast.Month, ast.Substr,
-		ast.Substring, ast.TimestampDiff, ast.DateFormat, ast.FromUnixTime:
+		ast.Substring, ast.TimestampDiff, ast.DateFormat, ast.FromUnixTime,
+		ast.JSONLength:
 		return true
 	case ast.Cast:
 		switch function.Function.PbCode() {