expression: fix the wrong behavior of conv function (#53681) (#53814)

close #53505

expression/builtin_math.go

@@ -1186,7 +1186,11 @@ func (b *builtinConvSig) evalString(row chunk.Row) (res string, isNull bool, err
 	switch x := b.args[0].(type) {
 	case *Constant:
 		if x.Value.Kind() == types.KindBinaryLiteral {
-			str = x.Value.GetBinaryLiteral().ToBitLiteralString(true)
+			datum, err := x.Eval(row)
+			if err != nil {
+				return "", false, err
+			}
+			str = datum.GetBinaryLiteral().ToBitLiteralString(true)
 		}
 	case *ScalarFunction:
 		if x.FuncName.L == ast.Cast {

planner/core/plan_cache_test.go

@@ -294,6 +294,20 @@ func TestIssue38710(t *testing.T) {
 	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0")) // can not use the cache because the types for @a and @b are not equal to the cached plan
 }
 
+func TestIssue53505(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec(`create table t (v varchar(16))`)
+	tk.MustExec(`insert into t values ('156')`)
+	tk.MustExec(`prepare stmt7 from 'select * from t where v = conv(?, 16, 8)'`)
+	tk.MustExec(`set @arg=0x6E`)
+	tk.MustQuery(`execute stmt7 using @arg`).Check(testkit.Rows("156"))
+	tk.MustQuery(`execute stmt7 using @arg`).Check(testkit.Rows("156"))
+	tk.MustExec(`set @arg=0x70`)
+	tk.MustQuery(`execute stmt7 using @arg`).Check(testkit.Rows()) // empty
+}
+
 func TestPlanCacheDiagInfo(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)