Function index and user_tab_cols

Why an entry is created in user_tab_cols when we create a function based on a column in a table?

 create table t1(a varchar2(100), b number);  


 select * from user_tab_cols where table_name = 'T1'; -- Two rows coming  


 create index idx1 on t1(upper(a)); 


 select * from user_tab_cols where table_name = 'T1'; -- Three rows coming

What is the reason to put an entry in user_tab_cols?

Martin Preiss wrote:

If I remember correctly there is also a VIRTUAL_COLUMN attribute in % _TAB_COLS (at least since 11.1).

Yes, there is, but how it would be useful to determine if the column is the index of based function related? All not stored in the disk column is a virtual column:

SQL > create table (tbl)
Number 2,
3 the number n
4                  )
5.

Table created.

SQL > create index tbl_idx1 on tbl (abs (n));

The index is created.

SQL > alter table tbl
2. Add n_ceil number generated always as (ceil (n));

Modified table.

SQL > alter table tbl change invisible n_ceil;

Modified table.

SQL > create index tbl_idx2 on tbl (n_ceil);

The index is created.

SQL > select column_id,.
2 column_name
virtual_column 3,.
4 hidden_column
5 to user_tab_cols
6 where table_name = "TBL";

COLUMN_ID COLUMN_NAME HIDDEN VIR
---------- ------------------------------ --- ---
1 ID                             NO  NO
2 N                              NO  NO
SYS_NC00003$ YES YES
N_CEIL YES YES

SQL >

As you can see, the two SYS_NC00003$ and N_CEIL are hidden, virtual columns. This part is the same regardless of the version. And in 12 c with the invisible support of solumn, you can't count on the id of null column. That's why (or at least one of the reasons) Oracle introduced another column in the view _TAB_COLS in 12 c - USER_GENERATED:

SQL > select column_id,.
2 column_name
virtual_column 3,.
hidden_column 4,.
5 user_generated
user_tab_cols 6
7 where table_name = "TBL";

COLUMN_ID COLUMN_NAME VIR HID USE
---------- ------------------------------ --- --- ---
1 NOT ONLY ID YES
2 N NO NO YES
SYS_NC00003$ YES YES NO
N_CEIL YES YES YES

SQL >

Now, we can say column SYS_NC00003$ is related FBI.

SY.

Tags: Database

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BANNER
----------------------------------------------------------------
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PL/SQL Release 10.2.0.3.0 - Production
CORE    10.2.0.3.0      Production
TNS for Linux: Version 10.2.0.3.0 - Production
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Execution Plan
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Plan hash value: 4202652051

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-------------

| Id  | Operation               | Name      | Rows  | Bytes |TempSpc| Cost (%CPU
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--------------------------------------------------------------------------------
-------------

|   0 | SELECT STATEMENT        |           |    10 |   740 |       |   504   (3
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   1 - filter(ROWNUM<11)
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        279  consistent gets
          0  physical reads
          0  redo size
        695  bytes sent via SQL*Net to client
        400  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          5  sorts (memory)
          0  sorts (disk)
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----------------------------------------------------------
Plan hash value: 1978014138

--------------------------------------------------------------------------------
------------------------

| Id  | Operation                      | Name          | Rows  | Bytes |TempSpc|
 Cost (%CPU)| Time     |

--------------------------------------------------------------------------------
------------------------

|   0 | SELECT STATEMENT               |               |    10 |   740 |       |
 22869   (1)| 00:04:35 |

|*  1 |  COUNT STOPKEY                 |               |       |       |       |
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|   2 |   VIEW                         |               | 49902 |  3606K|       |
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|*  3 |    SORT ORDER BY STOPKEY       |               | 49902 |  1559K|  3928K|
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------------------------


Predicate Information (identified by operation id):
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   1 - filter(ROWNUM<11)
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Statistics
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      22393  consistent gets
          0  physical reads
          0  redo size
        695  bytes sent via SQL*Net to client
        400  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
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From the explain ,the sql chooses the index,but SORT ORDER BY STOPKEY  doesn't avoid,so oracle
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Execution Plan
----------------------------------------------------------
Plan hash value: 4154852915

--------------------------------------------------------------------------------
---------------

| Id  | Operation                     | Name          | Rows  | Bytes | Cost (%C
PU)| Time     |

--------------------------------------------------------------------------------
---------------

|   0 | SELECT STATEMENT              |               |    10 |   740 |     8
(0)| 00:00:01 |

|*  1 |  COUNT STOPKEY                |               |       |       |
   |          |

|   2 |   VIEW                        |               |    10 |   740 |     8
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|   3 |    TABLE ACCESS BY INDEX ROWID| TEST_SORT     | 49902 |  1559K|     8
(0)| 00:00:01 |

|*  4 |     INDEX RANGE SCAN          | I_TEST_SORT_1 |    10 |       |     3
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--------------------------------------------------------------------------------
---------------


Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter(ROWNUM<11)
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Statistics
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          0  redo size
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        400  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
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          0  sorts (disk)
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