expression: fix the wrong behavior of conv function (#53681) (#54945)

close #53505

pkg/expression/builtin_math.go

@@ -1189,7 +1189,11 @@ func (b *builtinConvSig) evalString(ctx EvalContext, row chunk.Row) (res string,
 	switch x := b.args[0].(type) {
 	case *Constant:
 		if x.Value.Kind() == types.KindBinaryLiteral {
-			str = x.Value.GetBinaryLiteral().ToBitLiteralString(true)
+			datum, err := x.Eval(ctx, row)
+			if err != nil {
+				return "", false, err
+			}
+			str = datum.GetBinaryLiteral().ToBitLiteralString(true)
 		}
 	case *ScalarFunction:
 		if x.FuncName.L == ast.Cast {

pkg/planner/core/plan_cache_test.go

@@ -1253,6 +1253,20 @@ func TestPlanCacheBindingIgnore(t *testing.T) {
 	tk.MustQuery(`select @@last_plan_from_cache`).Check(testkit.Rows("0"))
 }
 
+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 TestBuiltinFuncFlen(t *testing.T) {
 	// same as TestIssue45378 and TestIssue45253
 	store := testkit.CreateMockStore(t)