`BatchGet` doesn't convert the type according to the column type.

[YangKeao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

func TestBatchGetType(t *testing.T) {
       ts := servertestkit.CreateTidbTestSuite(t)

       ts.RunTests(t, nil, func(dbt *testkit.DBTestKit) {
               dbt.MustExec("use test;")
               dbt.MustExec("create table t (id1 varchar(255) collate utf8mb4_general_ci, id2 varchar(255) collate utf8mb4_general_ci, primary key (id1, id2));")
               dbt.MustExec("insert into t values ('a', 'b'), ('c', 'd');")

               conn, err := dbt.GetDB().Conn(context.Background())
               require.NoError(t, err)
               defer func() {
                       require.NoError(t, conn.Close())
               }()

               conn.ExecContext(context.Background(), "set @@session.collation_connection = 'utf8mb4_general_ci'")
               stmt, err := conn.PrepareContext(context.Background(), "select * from t where (id1, id2) in ((?, ?), (?, ?))")
			   require.NoError(t, err)

			   rows, err := stmt.Query("A", "B", "C", "D");
			   require.NoError(t, err)

			   ts.CheckRows(t, rows, "a b\nc d")
       })
}

It used BatchGet. The parameter "?" has type "string collate utf8mb4_bin" (because TiDB doesn't set collation for parameter according to the connection collation. We should consider this issue later). Reference:

tidb/pkg/planner/core/point_get_plan.go

Line 1818 in 7424255

dVal, err := d.ConvertTo(evalCtx.TypeCtx(), &col.FieldType)

2. What did you expect to see? (Required)

The test pass

3. What did you see instead (Required)

The test failed

4. What is your TiDB version? (Required)

[YangKeao]

This bug only affects RowExpr (which means multiple columns) and BatchGet. For a single column, it's implemented correctly. I think it's a typo 🤔 .