From c9731573efac05361828e6749dc3dd03ed046de9 Mon Sep 17 00:00:00 2001
From: yibin <huyibin@pingcap.com>
Date: Thu, 23 May 2024 18:43:21 +0800
Subject: [PATCH] expression: Disallow conv fuction with hybrid type argement
 to be pushed down to TiKV (#53502)

close pingcap/tidb#51877
---
 pkg/expression/expr_to_pb_test.go | 19 +++++++++++++++++++
 pkg/expression/infer_pushdown.go  | 13 ++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/pkg/expression/expr_to_pb_test.go b/pkg/expression/expr_to_pb_test.go
index f912e5f6e4d91..d64af182e2e69 100644
--- a/pkg/expression/expr_to_pb_test.go
+++ b/pkg/expression/expr_to_pb_test.go
@@ -1456,6 +1456,7 @@ func TestExprPushDownToTiKV(t *testing.T) {
 	//datetimeColumn := genColumn(mysql.TypeDatetime, 6)
 	binaryStringColumn := genColumn(mysql.TypeString, 7)
 	dateColumn := genColumn(mysql.TypeDate, 8)
+	byteColumn := genColumn(mysql.TypeBit, 9)
 	binaryStringColumn.RetType.SetCollate(charset.CollationBin)
 
 	// Test exprs that cannot be pushed.
@@ -1497,6 +1498,24 @@ func TestExprPushDownToTiKV(t *testing.T) {
 	require.Len(t, pushed, 0)
 	require.Len(t, remained, len(exprs))
 
+	// Test Conv function
+	exprs = exprs[:0]
+	function, err = NewFunction(mock.NewContext(), ast.Conv, types.NewFieldType(mysql.TypeString), stringColumn, intColumn, intColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+	pushed, remained = PushDownExprs(pushDownCtx, exprs, kv.TiKV)
+	require.Len(t, pushed, len(exprs))
+	require.Len(t, remained, 0)
+	exprs = exprs[:0]
+	castByteAsStringFunc, err := NewFunction(mock.NewContext(), ast.Cast, types.NewFieldType(mysql.TypeString), byteColumn)
+	require.NoError(t, err)
+	function, err = NewFunction(mock.NewContext(), ast.Conv, types.NewFieldType(mysql.TypeString), castByteAsStringFunc, intColumn, intColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+	pushed, remained = PushDownExprs(pushDownCtx, exprs, kv.TiKV)
+	require.Len(t, pushed, 0)
+	require.Len(t, remained, len(exprs))
+
 	// Test exprs that can be pushed.
 	exprs = exprs[:0]
 	pushed = pushed[:0]
diff --git a/pkg/expression/infer_pushdown.go b/pkg/expression/infer_pushdown.go
index ab50c1a2adb60..dbcef86688935 100644
--- a/pkg/expression/infer_pushdown.go
+++ b/pkg/expression/infer_pushdown.go
@@ -177,7 +177,7 @@ func scalarExprSupportedByTiKV(sf *ScalarFunction) bool {
 		// Rust use the llvm math functions, which have different precision with Golang/MySQL(cmath)
 		// open the following switchers if we implement them in coprocessor via `cmath`
 		ast.Sin, ast.Asin, ast.Cos, ast.Acos /* ast.Tan */, ast.Atan, ast.Atan2, ast.Cot,
-		ast.Radians, ast.Degrees, ast.Conv, ast.CRC32,
+		ast.Radians, ast.Degrees, ast.CRC32,
 
 		// control flow functions.
 		ast.Case, ast.If, ast.Ifnull, ast.Coalesce,
@@ -221,6 +221,17 @@ func scalarExprSupportedByTiKV(sf *ScalarFunction) bool {
 		/*ast.InetNtoa, ast.InetAton, ast.Inet6Ntoa, ast.Inet6Aton, ast.IsIPv4, ast.IsIPv4Compat, ast.IsIPv4Mapped, ast.IsIPv6,*/
 		ast.UUID:
 
+		return true
+	// Rust use the llvm math functions, which have different precision with Golang/MySQL(cmath)
+	// open the following switchers if we implement them in coprocessor via `cmath`
+	case ast.Conv:
+		arg0 := sf.GetArgs()[0]
+		// To be aligned with MySQL, tidb handles hybrid type argument and binary literal specially, tikv can't be consistent with tidb now.
+		if f, ok := arg0.(*ScalarFunction); ok {
+			if f.FuncName.L == ast.Cast && (f.GetArgs()[0].GetType().Hybrid() || IsBinaryLiteral(f.GetArgs()[0])) {
+				return false
+			}
+		}
 		return true
 	case ast.Round:
 		switch sf.Function.PbCode() {