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| 1 | - | create table tt as select rownum id, t.* from dba_objects where rownum < 100000; |
| 1 | + | create table tt as select rownum id, t.* from dba_objects t where rownum < 100000; |
| 2 | ||
| 3 | insert into tt as select * from tt; | |
| 4 | ||
| 5 | insert into tt as select * from tt; | |
| 6 | ||
| 7 | commit; | |
| 8 | ||
| 9 | set autot on exp stat | |
| 10 | SQL> select count(distinct id) from tt; | |
| 11 | ||
| 12 | COUNT(DISTINCTID) | |
| 13 | ----------------- | |
| 14 | 999999 | |
| 15 | ||
| 16 | Elapsed: 00:00:02.15 | |
| 17 | ||
| 18 | Execution Plan | |
| 19 | ---------------------------------------------------------- | |
| 20 | Plan hash value: 1056889062 | |
| 21 | ||
| 22 | ----------------------------------------------------------------------------------------- | |
| 23 | | Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | | |
| 24 | ----------------------------------------------------------------------------------------- | |
| 25 | | 0 | SELECT STATEMENT | | 1 | 13 | | 6834 (1)| 00:00:01 | | |
| 26 | | 1 | SORT AGGREGATE | | 1 | 13 | | | | | |
| 27 | | 2 | VIEW | VW_DAG_0 | 999K| 12M| | 6834 (1)| 00:00:01 | | |
| 28 | | 3 | HASH GROUP BY | | 999K| 4882K| 11M| 6834 (1)| 00:00:01 | | |
| 29 | | 4 | TABLE ACCESS FULL| TT | 999K| 4882K| | 3769 (1)| 00:00:01 | | |
| 30 | ----------------------------------------------------------------------------------------- | |
| 31 | ||
| 32 | ||
| 33 | Statistics | |
| 34 | ---------------------------------------------------------- | |
| 35 | 0 recursive calls | |
| 36 | 0 db block gets | |
| 37 | 95708 consistent gets | |
| 38 | 54725 physical reads | |
| 39 | 0 redo size | |
| 40 | 553 bytes sent via SQL*Net to client | |
| 41 | 552 bytes received via SQL*Net from client | |
| 42 | 2 SQL*Net roundtrips to/from client | |
| 43 | 0 sorts (memory) | |
| 44 | 0 sorts (disk) | |
| 45 | 1 rows processed | |
| 46 | ||
| 47 | ||
| 48 | SQL> SELECT APPROX_COUNT_DISTINCT(id) from tt; | |
| 49 | ||
| 50 | APPROX_COUNT_DISTINCT(ID) | |
| 51 | ------------------------- | |
| 52 | 971092 | |
| 53 | ||
| 54 | Elapsed: 00:00:00.71 | |
| 55 | ||
| 56 | Execution Plan | |
| 57 | ---------------------------------------------------------- | |
| 58 | Plan hash value: 3133740314 | |
| 59 | ||
| 60 | ------------------------------------------------------------------------------ | |
| 61 | | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | | |
| 62 | ------------------------------------------------------------------------------ | |
| 63 | | 0 | SELECT STATEMENT | | 1 | 5 | 3769 (1)| 00:00:01 | | |
| 64 | | 1 | SORT AGGREGATE APPROX| | 1 | 5 | | | | |
| 65 | | 2 | TABLE ACCESS FULL | TT | 999K| 4882K| 3769 (1)| 00:00:01 | | |
| 66 | ------------------------------------------------------------------------------ | |
| 67 | ||
| 68 | ||
| 69 | Statistics | |
| 70 | ---------------------------------------------------------- | |
| 71 | 5 recursive calls | |
| 72 | 0 db block gets | |
| 73 | 95710 consistent gets | |
| 74 | 54725 physical reads | |
| 75 | 0 redo size | |
| 76 | 561 bytes sent via SQL*Net to client | |
| 77 | 552 bytes received via SQL*Net from client | |
| 78 | 2 SQL*Net roundtrips to/from client | |
| 79 | 0 sorts (memory) | |
| 80 | 0 sorts (disk) | |
| 81 | 1 rows processed |
