Why plan table showing 1 rec

Question

SQL> CREATE TABLE A (ID NUMBER)
2 /
Table created.
SQL> EXPLAIN PLAN FOR SELECT * FROM A
2 /
Explained.
SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY)
2 /
PLAN_TABLE_OUTPUT
Plan hash value: 1222032187
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS FULL| A | 1 | 13 | 2 (0)| 00:00:01 |
Note
PLAN_TABLE_OUTPUT
- dynamic sampling used for this statement
12 rows selected.
why plan table showing one record when i have no record in table a.
regards

Answer 1

This is because you did not analyze the table, and if it was analyzed, it maps a zero to a one. Please not that my test is not in 10g but on 9iR2, where non analyzed tables have null values in their estimated cardinalities.
SQL> create table a (id number)
  2  /
Tabel is aangemaakt.
SQL> explain plan for select * from a
  2  /
Uitleg is gegeven.
SQL> select * from table(dbms_xplan.display)
  2  /
PLAN_TABLE_OUTPUT
| Id  | Operation            |  Name       | Rows  | Bytes | Cost  |
|   0 | SELECT STATEMENT     |             |       |       |       |
|   1 |  TABLE ACCESS FULL   | A           |       |       |       |
Note: rule based optimization
9 rijen zijn geselecteerd.
SQL> exec dbms_lock.sleep(1)
PL/SQL-procedure is geslaagd.
SQL> insert into a values (1)
  2  /
1 rij is aangemaakt.
SQL> explain plan for select * from a
  2  /
Uitleg is gegeven.
SQL> select * from table(dbms_xplan.display)
  2  /
PLAN_TABLE_OUTPUT
| Id  | Operation            |  Name       | Rows  | Bytes | Cost  |
|   0 | SELECT STATEMENT     |             |       |       |       |
|   1 |  TABLE ACCESS FULL   | A           |       |       |       |
Note: rule based optimization
9 rijen zijn geselecteerd.
SQL> exec dbms_lock.sleep(1)
PL/SQL-procedure is geslaagd.
SQL> insert into a select level from dual connect by level <= 9
  2  /
9 rijen zijn aangemaakt.
SQL> explain plan for select * from a
  2  /
Uitleg is gegeven.
SQL> select * from table(dbms_xplan.display)
  2  /
PLAN_TABLE_OUTPUT
| Id  | Operation            |  Name       | Rows  | Bytes | Cost  |
|   0 | SELECT STATEMENT     |             |       |       |       |
|   1 |  TABLE ACCESS FULL   | A           |       |       |       |
Note: rule based optimization
9 rijen zijn geselecteerd.
SQL> exec dbms_lock.sleep(1)
PL/SQL-procedure is geslaagd.
SQL> truncate table a
  2  /
Tabel is afgekapt.
SQL> exec dbms_stats.gather_table_stats(user,'A')
PL/SQL-procedure is geslaagd.
SQL> explain plan for select * from a
  2  /
Uitleg is gegeven.
SQL> select * from table(dbms_xplan.display)
  2  /
PLAN_TABLE_OUTPUT
| Id  | Operation            |  Name       | Rows  | Bytes | Cost (%CPU)|
|   0 | SELECT STATEMENT     |             |     1 |    13 |     3  (34)|
|   1 |  TABLE ACCESS FULL   | A           |     1 |    13 |     3  (34)|
7 rijen zijn geselecteerd.
SQL> exec dbms_lock.sleep(1)
PL/SQL-procedure is geslaagd.
SQL> insert into a values (1)
  2  /
1 rij is aangemaakt.
SQL> exec dbms_stats.gather_table_stats(user,'A')
PL/SQL-procedure is geslaagd.
SQL> explain plan for select * from a
  2  /
Uitleg is gegeven.
SQL> select * from table(dbms_xplan.display)
  2  /
PLAN_TABLE_OUTPUT
| Id  | Operation            |  Name       | Rows  | Bytes | Cost (%CPU)|
|   0 | SELECT STATEMENT     |             |     1 |     3 |     3  (34)|
|   1 |  TABLE ACCESS FULL   | A           |     1 |     3 |     3  (34)|
7 rijen zijn geselecteerd.
SQL> exec dbms_lock.sleep(1)
PL/SQL-procedure is geslaagd.
SQL> insert into a select level from dual connect by level <= 9
  2  /
9 rijen zijn aangemaakt.
SQL> exec dbms_stats.gather_table_stats(user,'A')
PL/SQL-procedure is geslaagd.
SQL> explain plan for select * from a
  2  /
Uitleg is gegeven.
SQL> select * from table(dbms_xplan.display)
  2  /
PLAN_TABLE_OUTPUT
| Id  | Operation            |  Name       | Rows  | Bytes | Cost (%CPU)|
|   0 | SELECT STATEMENT     |             |    10 |    30 |     3  (34)|
|   1 |  TABLE ACCESS FULL   | A           |    10 |    30 |     3  (34)|
7 rijen zijn geselecteerd.Regards,
Rob.