*: TIDB_DECODE_KEY(): Decode keys which only have a TableID

expression/integration_test.go

@@ -4996,16 +4996,23 @@ func (s *testIntegrationSuite) TestTiDBInternalFunc(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	defer s.cleanEnv(c)
 	var result *testkit.Result
+
+	// Row Keys
 	result = tk.MustQuery("select tidb_decode_key( '74800000000000002B5F72800000000000A5D3' )")
 	result.Check(testkit.Rows(`{"_tidb_rowid":42451,"table_id":"43"}`))
 	result = tk.MustQuery("select tidb_decode_key( '7480000000000000325f7205bff199999999999a013131000000000000f9' )")
 	result.Check(testkit.Rows(`{"handle":"{1.1, 11}","table_id":50}`))
 
+	// Index Keys
 	result = tk.MustQuery("select tidb_decode_key( '74800000000000019B5F698000000000000001015257303100000000FB013736383232313130FF3900000000000000F8010000000000000000F7' )")
 	result.Check(testkit.Rows(`{"index_id":1,"index_vals":"RW01, 768221109, ","table_id":411}`))
 	result = tk.MustQuery("select tidb_decode_key( '7480000000000000695F698000000000000001038000000000004E20' )")
 	result.Check(testkit.Rows(`{"index_id":1,"index_vals":"20000","table_id":105}`))
 
+	// Table keys
+	result = tk.MustQuery("select tidb_decode_key( '7480000000000000FF4700000000000000F8' )")
+	result.Check(testkit.Rows(`{"table_id":71}`))
+
 	// Test invalid record/index key.
 	result = tk.MustQuery("select tidb_decode_key( '7480000000000000FF2E5F728000000011FFE1A3000000000000' )")
 	result.Check(testkit.Rows("7480000000000000FF2E5F728000000011FFE1A3000000000000"))

planner/core/expression_rewriter.go

@@ -2007,6 +2007,13 @@ func decodeKeyFromString(ctx sessionctx.Context, s string) string {
 			return s
 		}
 		return ret
+	} else if tablecodec.IsTableKey(key) {
+		ret, err := decodeTableKey(key, tableID, tbl, loc)
+		if err != nil {
+			ctx.GetSessionVars().StmtCtx.AppendWarning(err)
+			return s
+		}
+		return ret
 	}
 	ctx.GetSessionVars().StmtCtx.AppendWarning(errors.Errorf("invalid record/index key: %X", key))
 	return s
@@ -2150,6 +2157,16 @@ func decodeIndexKey(key []byte, tableID int64, tbl table.Table, loc *time.Locati
 	return string(retStr), nil
 }
 
+func decodeTableKey(key []byte, tableID int64, tbl table.Table, loc *time.Location) (string, error) {
+	ret := make(map[string]interface{})
+	ret["table_id"] = tableID
+	retStr, err := json.Marshal(ret)
+	if err != nil {
+		return "", errors.Trace(err)
+	}
+	return string(retStr), nil
+}
+
 func datumToJSONObject(d *types.Datum) (interface{}, error) {
 	if d.IsNull() {
 		return nil, nil

tablecodec/tablecodec.go

@@ -980,6 +980,11 @@ func IsIndexKey(k []byte) bool {
 	return len(k) > 11 && k[0] == 't' && k[10] == 'i'
 }
 
+// IsTableKey is used to check whether the key is a table key.
+func IsTableKey(k []byte) bool {
+	return len(k) == 9 && k[0] == 't'
+}
+
 // IsUntouchedIndexKValue uses to check whether the key is index key, and the value is untouched,
 // since the untouched index key/value is no need to commit.
 func IsUntouchedIndexKValue(k, v []byte) bool {