From 8e80e7c96cf0c75c26244bd8a18e727fb8e45ac1 Mon Sep 17 00:00:00 2001
From: baishen <baishen2009@gmail.com>
Date: Fri, 30 Dec 2022 14:06:18 +0800
Subject: [PATCH] expression: implement `unhex` function pushdown to tiflash
 (#39898)

ref pingcap/tidb#5112, ref pingcap/tiflash#5112
---
 expression/expr_to_pb_test.go    |  5 +++++
 expression/expression.go         |  2 +-
 planner/core/integration_test.go | 33 ++++++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/expression/expr_to_pb_test.go b/expression/expr_to_pb_test.go
index 1025f3c7fdcb1..341c03b552804 100644
--- a/expression/expr_to_pb_test.go
+++ b/expression/expr_to_pb_test.go
@@ -1239,6 +1239,11 @@ func TestExprPushDownToFlash(t *testing.T) {
 	require.Equal(t, tipb.ScalarFuncSig_CastTimeAsDuration, function.(*ScalarFunction).Function.PbCode())
 	exprs = append(exprs, function)
 
+	// Unhex
+	function, err = NewFunction(mock.NewContext(), ast.Unhex, types.NewFieldType(mysql.TypeString), stringColumn)
+	require.NoError(t, err)
+	exprs = append(exprs, function)
+
 	pushed, remained = PushDownExprs(sc, exprs, client, kv.TiFlash)
 	require.Len(t, pushed, len(exprs))
 	require.Len(t, remained, 0)
diff --git a/expression/expression.go b/expression/expression.go
index c7ce0b22c1c0e..00697c2df68ea 100644
--- a/expression/expression.go
+++ b/expression/expression.go
@@ -1267,7 +1267,7 @@ func scalarExprSupportedByFlash(function *ScalarFunction) bool {
 		}
 	case ast.IsTruthWithNull, ast.IsTruthWithoutNull, ast.IsFalsity:
 		return true
-	case ast.Hex, ast.Bin:
+	case ast.Hex, ast.Unhex, ast.Bin:
 		return true
 	case ast.GetFormat:
 		return true
diff --git a/planner/core/integration_test.go b/planner/core/integration_test.go
index 31cd5aa9c346b..307971e2d77e1 100644
--- a/planner/core/integration_test.go
+++ b/planner/core/integration_test.go
@@ -7520,6 +7520,39 @@ func TestCastTimeAsDurationToTiFlash(t *testing.T) {
 	tk.MustQuery("explain select cast(a as time), cast(b as time) from t;").CheckAt([]int{0, 2, 4}, rows)
 }
 
+func TestUnhexPushDownToTiFlash(t *testing.T) {
+	store, dom := testkit.CreateMockStoreAndDomain(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int, b varchar(20));")
+	tk.MustExec("insert into t values(6162, '7469666C617368');")
+	tk.MustExec("set @@tidb_allow_mpp=1; set @@tidb_enforce_mpp=1;")
+	tk.MustExec("set @@tidb_isolation_read_engines = 'tiflash'")
+
+	tbl, err := dom.InfoSchema().TableByName(model.CIStr{O: "test", L: "test"}, model.CIStr{O: "t", L: "t"})
+	require.NoError(t, err)
+	// Set the hacked TiFlash replica for explain tests.
+	tbl.Meta().TiFlashReplica = &model.TiFlashReplicaInfo{Count: 1, Available: true}
+
+	rows := [][]interface{}{
+		{"TableReader_9", "root", "data:ExchangeSender_8"},
+		{"└─ExchangeSender_8", "mpp[tiflash]", "ExchangeType: PassThrough"},
+		{"  └─Projection_4", "mpp[tiflash]", "unhex(cast(test.t.a, var_string(20)))->Column#4"},
+		{"    └─TableFullScan_7", "mpp[tiflash]", "keep order:false, stats:pseudo"},
+	}
+	tk.MustQuery("explain select unhex(a) from t;").CheckAt([]int{0, 2, 4}, rows)
+
+	rows = [][]interface{}{
+		{"TableReader_9", "root", "data:ExchangeSender_8"},
+		{"└─ExchangeSender_8", "mpp[tiflash]", "ExchangeType: PassThrough"},
+		{"  └─Projection_4", "mpp[tiflash]", "unhex(test.t.b)->Column#4"},
+		{"    └─TableFullScan_7", "mpp[tiflash]", "keep order:false, stats:pseudo"},
+	}
+	tk.MustQuery("explain select unhex(b) from t;").CheckAt([]int{0, 2, 4}, rows)
+}
+
 func TestPartitionTableFallBackStatic(t *testing.T) {
 	store, _ := testkit.CreateMockStoreAndDomain(t)
 	tk := testkit.NewTestKit(t, store)