planner: add more test cases for non-prep plan cache (#42015)

ref #36598

Author: qw4990

planner/core/plan_cache.go

@@ -53,6 +53,7 @@ func planCachePreprocess(ctx context.Context, sctx sessionctx.Context, isNonPrep
 	}
 
 	// step 2: set parameter values
+	vars.PreparedParams = vars.PreparedParams[:0]
 	for i, usingParam := range params {
 		val, err := usingParam.Eval(chunk.Row{})
 		if err != nil {

planner/core/plan_cache_test.go

@@ -26,7 +26,9 @@ import (
 	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/parser/mysql"
+	"github.com/pingcap/tidb/planner"
 	plannercore "github.com/pingcap/tidb/planner/core"
+	"github.com/pingcap/tidb/session"
 	"github.com/pingcap/tidb/testkit"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util"
@@ -136,6 +138,35 @@ func TestIssue40296(t *testing.T) {
 	tk.MustQuery("select @@last_plan_from_cache").Check(testkit.Rows("0")) // unary operator '-' is not supported now.
 }
 
+func TestNonPreparedPlanCachePlanString(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec(`use test`)
+	tk.MustExec(`create table t (a int, b int, key(a))`)
+	tk.MustExec(`set @@tidb_enable_non_prepared_plan_cache=1`)
+
+	ctx := tk.Session()
+	planString := func(sql string) string {
+		stmts, err := session.Parse(ctx, sql)
+		require.NoError(t, err)
+		stmt := stmts[0]
+		ret := &plannercore.PreprocessorReturn{}
+		err = plannercore.Preprocess(context.Background(), ctx, stmt, plannercore.WithPreprocessorReturn(ret))
+		require.NoError(t, err)
+		p, _, err := planner.Optimize(context.TODO(), ctx, stmt, ret.InfoSchema)
+		require.NoError(t, err)
+		return plannercore.ToString(p)
+	}
+
+	require.Equal(t, planString("select a from t where a < 1"), "IndexReader(Index(t.a)[[-inf,1)])")
+	require.Equal(t, planString("select a from t where a < 10"), "IndexReader(Index(t.a)[[-inf,10)])") // range 1 -> 10
+	tk.MustQuery(`select @@last_plan_from_cache`).Check(testkit.Rows("1"))
+
+	require.Equal(t, planString("select * from t where b < 1"), "TableReader(Table(t)->Sel([lt(test.t.b, 1)]))")
+	require.Equal(t, planString("select * from t where b < 10"), "TableReader(Table(t)->Sel([lt(test.t.b, 10)]))") // filter 1 -> 10
+	tk.MustQuery(`select @@last_plan_from_cache`).Check(testkit.Rows("1"))
+}
+
 func TestNonPreparedPlanCacheJSONFilter(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)