Similar Questions

• ORA-54002 on creating virtual column

  I wonder on what follows.

  I'm in the middle of a migration project.

  I load the data received from the source database into the staging tables.

  The data in these tables must remain absolutely intact to be able to check where things have gone wrong if something is not the way we expected after migration.

  Obviously, the data includes dates. Those who are in the DATE data type columns.

  However, the values represent the date and time UTC.

  The values are NOT timestamps with time zone, but simply date that contains the date time and something that has passed, but expressed in the date and time utc.

  Now, the database target also expects that DATEs, so I seem to be home free.

  However, the target database expect the passage of time to express the time zones (Europe/Amsterdam).

  No problem I know how to do this.

  And because I want to do a million times in the transformation before insertion in the target code (and almost certainly forget a few times) I thought: I'll add virtual columns for the staging tables that allow to calculate the local time of the date and time utc.

  This way the data is intact, but the transformation code can simply use the column (virtual) replacement and does not bother with the calculations of time.

  Great, I thought.

  Until I tried to create the table.

  CREATE TABLE utc_test

  (createddate_utc DATE

  createddate GENERATED DATE ALWAYS

  AS (CAST (FROM_TZ (CAST (createddate_utc AS TIMESTAMP)

  , "UTC".

  )

  At the time of the ZONE "Europe/Amsterdam".

  AS DATE

  )

  )

  VIRTUAL

  );

  And Oracle says:

  At the time of the ZONE "Europe/Amsterdam".

  *

  ERROR on line 7:

  ORA-54002: only pure functions can be specified in a virtual column expression

  Excuse me?

  Not deterministic?

  Oracle is probably right, and even if it isn't yet I have to live with that.

  But no matter how hard I try I can't understand why this code would not deterministic.

  IMHO any form of date I put in createddate_utc, if I put the same date in here a million times I'll get the same answer a million times.

  I know, FROM_TZ to the ZONE SCHEDULE will give different answers for different time zones.

  But not for a same time zone.

  And is this not the essence of deterministic: always the same result, given the same input?

  Anyone who can teach me Oracle ;-)

  My question (I may not was clear on that) was: why Oracle claims that the function is not deterministic?

  Because this is not the case.

  Zone information (and therefore the conversion between TZs) are governed by the zone files, see: Datetime and time zones Support Data Types.

  Since these data may vary, it is not deterministic.

  To solve this 'problem', you can always create a standalone function transformation of packaging and declare it deterministic, even if it is not in the strict sense.

• Addition of virtual column: ORA-12899: value too large for column

  I am using Oracle 11g, OS Win7, SQL Developer
  
  I'm trying to add the virtual column to my test table, but get ORA-12899: value too large for column error. Here are the details.
  Can someone help me in this?
  

  CREATE TABLE test_reg_exp
  (col1 VARCHAR2(100));
  
  INSERT INTO test_reg_exp (col1) VALUES ('ABCD_EFGH');
  INSERT INTO test_reg_exp (col1) VALUES ('ABCDE_ABC');
  INSERT INTO test_reg_exp (col1) VALUES ('WXYZ_ABCD');
  INSERT INTO test_reg_exp (col1) VALUES ('ABCDE_PQRS');
  INSERT INTO test_reg_exp (col1) VALUES ('ABCD_WXYZ');

  ALTER TABLE test_reg_exp
  ADD (col2 VARCHAR2(100) GENERATED ALWAYS AS (REGEXP_REPLACE (col1, '^ABCD[A-Z]*_')));
  
  SQL Error: ORA-12899: value too large for column "COL2" (actual: 100, maximum: 400)
  12899. 00000 -  "value too large for column %s (actual: %s, maximum: %s)"
  *Cause:    An attempt was made to insert or update a column with a value
             which is too wide for the width of the destination column.
             The name of the column is given, along with the actual width
             of the value, and the maximum allowed width of the column.
             Note that widths are reported in characters if character length
             semantics are in effect for the column, otherwise widths are
             reported in bytes.
  *Action:   Examine the SQL statement for correctness.  Check source
             and destination column data types.
             Either make the destination column wider, or use a subset
             of the source column (i.e. use substring).

  When I try to, I get the correct results:
  

  SELECT col1, (REGEXP_REPLACE (col1, '^ABCD[A-Z]*_'))
  FROM test_reg_exp;

  Thank you.

  Yes, RP, it works if you give col2 size > = 400.

  @Northwest - could you please test the same w/o having a clause of regex in col2?
  I have a doubt about using a REGULAR expression in this case Dynamics col.

  Refer to this (might help) - http://www.oracle-base.com/articles/11g/virtual-columns-11gr1.php
  Below excerpt from above link... see if that helps...
  >
  Notes and restrictions on the virtual columns include:

  The indexes defined on the virtual columns are equivalent to a function-based index.
  Virtual columns can be referenced in the updates and deletions WHERE clause, but they cannot be manipulated by DML.
  The tables containing virtual columns may still be eligible for result caching.
  Functions in expressions must be deterministic when the table is created, but can then be recompiled and non-deterministic without for as much invalidate the virtual column. In such cases, the following steps must be taken after the function is recompiled:
  Constraint on the virtual column must be disabled and re-enabled.
  On the virtual column indexes must be rebuilt.
  Materialized views that access the virtual column must be fully refreshed.
  The result cache must be flushed if the virtual column acceded to the request (s).
  Statistical table must be regathered.
  The virtual columns are not supported for the organized and external object in index, cluster or temporary tables.
  The expression used in the virtual column definition has the following restrictions:
  It cannot refer to another virtual column by name.
  It can refer to the columns defined in the same table.
  If it refers to a deterministic user-defined function, it cannot be used as a partitioning key column.
  The result of the expression must be a scalar value. It cannot return that an Oracle supplied the data type, a type defined by the user, LOB or LONG RAW.
  >

  Published by: Vanessa B on October 16, 2012 23:48

  Published by: Vanessa B on October 16, 2012 23:54

• Interval partitioning using the key of the virtual column

  Hi guys

  I have a series of tables that I propose to the partition.

  Each table has a year and a period (equivalent to a month) and I intend using those as my partition keys - year as the partition and the period as the subpartition.

  The distribution will be actually:

  2015

  001

  002

  ...

  012

  2016

  001

  002

  ...

  012

  etc...

  I would use range partitioning for the year, because it would make the maintenance of the partition a breeze.  Only one problem - the field is of type varchar, and is not modifiable as its legacy applications that have become bigger than Ben Hurr and more tangled than a Ben Hurr size flat spaghetti.

  It is hence the idea of virtual column between in game - I could create a virtual column in these tables to convert the field to digital and then partition on it instead.

  My question-if the year of origin varchar column is included in the where clause of a query, is the optimizer based on CSSTidy smart enough to realize that the virtual column used for the partition key is based on this column and use pruning of partition to improve performance?  Or queries must refer to the virtual column to make it work?  Also, the virtual column should be indexed to make it work?

  Thanks in advance.

  
  

  Simon
  

  orclz >

  orclz > create table pt (v1 varchar2 (1) c1 as (to_number (v1)), number of c2)

  2 partition by range (c1) interval (1)

  subpartition by hash (c2) subpartitions 4 3

  4 (partition p1 values less than (1))

  5.

  Table created.

  orclz > set autot on explain

  orclz > select * PT where v1 = '0';

  no selected line

  Execution plan

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

  Hash value of plan: 711571056

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

  | ID | Operation | Name | Lines | Bytes | Cost (% CPU). Time | Pstart. Pstop |

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

  |  0 | SELECT STATEMENT |      |    82.  2296 |    29 (0) | 00:00:01 |      |      |

  |  1.  RANGE OF PARTITION ALL THE |      |    82.  2296 |    29 (0) | 00:00:01 |    1. 1048575.

  |  2.  HASH PARTITION ALL |      |    82.  2296 |    29 (0) | 00:00:01 |    1.    4.

  |*  3 |    TABLE ACCESS FULL | PT |    82.  2296 |    29 (0) | 00:00:01 |    1. 1048575.

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

  Information of predicates (identified by the operation identity card):

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

  3 - filter ("V1" = '0')

  orclz > select * PT where c1 = 0;

  no selected line

  Execution plan

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

  Hash value of plan: 1726115854

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

  | ID | Operation | Name | Lines | Bytes | Cost (% CPU). Time | Pstart. Pstop |

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

  |  0 | SELECT STATEMENT |      |    82.  2296 |    29 (0) | 00:00:01 |      |      |

  |  1.  RANGE OF SINGLE PARTITION |      |    82.  2296 |    29 (0) | 00:00:01 |    1.    1.

  |  2.  HASH PARTITION ALL |      |    82.  2296 |    29 (0) | 00:00:01 |    1.    4.

  |*  3 |    TABLE ACCESS FULL | PT |    82.  2296 |    29 (0) | 00:00:01 |    1.    4.

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

  Information of predicates (identified by the operation identity card):

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

  3 - filter ("C1" = 0)

  --

  John Watson

  Oracle Certified Master s/n

• Convert a Non-virtual virtual column

  Can I convert a virtual column in a non-virtual (ordinary scalar column) or what I have to delete and recreate?

  for example, I have a virtual column defined as:

  exam_length NUMBER GENERATED ALWAYS AS ("TOTAL_SESSION_LENGTH"-NVL("TUTORIAL_LENGTH",0)-NVL("SURVEY_LENGTH",0) "")

  and I just want to:

  exam_length NUMBER (10.0)

  
  

  I tried:
  

  ALTER TABLE my_table () CHANGE

  EXAM_LENGTH NUMBER (10,0))

  /

  ... but that just change the data type and keeps virtual with the product still intact clause

  You would have to

  a. Add a new column (regular)

  b. copy the virtual column to the new column data

  c. drop the virtual column

  d. rename the new column

  Hemant K Chitae

• json_list to varchar/string to use in the virtual column

  Hello Experts,

  Environment:

  Database Oracle 12 c Enterprise Edition Release 12.1.0.2.0 - 64 bit Production

  PL/SQL Release 12.1.0.2.0 - Production

  I have the following function that returns JSON_LIST.

  {code}

  CREATE OR REPLACE FUNCTION GENERATE_JSON (STRING2CONVERT IN VARCHAR2)

  RETURN JSON_LIST

  DETERMINISTIC

  IS

  RET json_list;

  V_ERROR VARCHAR2 (31000);

  BEGIN

  RET: = json_dyn.executeList (STRING2CONVERT);

  RET. Print;

  RETURN RET;

  EXCEPTION WHEN OTHERS THEN

  V_ERROR: = SQLERRM;

  RETURNS A NULL VALUE.

  END;

  -test the query see the output in the output of DBMS

  SELECT GENERATE_JSON (' select ' |) Chr (39) | ' AJ' | Chr (39) |' like c_name,' | Chr (39) | ' BOY ' | Chr (39): ' c_type, like '

  || Chr (39) | ' HUMAN '. Chr (39): ' as c_category,' | Chr (39) | ' TEST SUBJECT ' | Chr (39) | 'as c_desc from dual')

  FROM DUAL;

  
  

  {code}

  
  

  The SQL query above in the DBMS output output

  [{

  "C_NAME": "AJ."

  "C_TYPE": "BOY."

  "C_CATEGORY": "HUMAN."

  'C_DESC': 'GUINEA PIG '.

  }]

  
  

  Question: How can I have it return the same structure of String (varchar).
  

  
  

  Why would I want to convert JSON_LIST to string?

  So that I can use this call to service as part of a virtual column in a table to store Json and have a constraint to enforce structureof Json.

  
  

  If this is not the right way?

  Kindly share how I can take a few columns in the same table, convert to json format and store in a virtual column in the same table and enforce the Json structure?

  
  

  Thank you

  AJ
  

  
  

  
  

  with

  data in the form of

  (select q'~ select "AJ" as c_name, 'BOY' as c_type, 'HUMAN' as c_category, 'SUBJECT of TEST' as the double c_desc ~' source)

  of the double

  ),

  Converter (SRC, res, Step) as

  (select regexp_replace (ltrim (upper (substr (source, 1, instr (upper (source), "FROM") - 1)), "SELECT"), '\s+AS\s+',': ') |) ',', null, 1

  from the data

  Union of all the

  Select substr (src, instr(src,',') + 1)

  '"' || substr (substr (SRC, 1, InStr (CBC, ',') - 1), instr (substr (src, 1, instr (CBC, ',') - 1),': ') + 1) | '" : ' ||

  Replace (substr (substr (SRC, 1, InStr (CBC, ',') - 1), 1, instr (substr (src, 1, instr (CBC, ',') - 1),': ')-1), "','" ' "),

  Step + 1

  converter

  where the CBC is not null

  )

  Select the source'[{' | listagg(res,',') Group (order by step) |}] '] "converted

  data converter

  SOURCE	CONVERTED
  Select "AJ" as c_name, 'BOY' as c_type, 'HUMAN' as c_category, 'SUBJECT of TEST' as double c_desc	[{'C_NAME': 'AJ', 'C_TYPE': 'BOY', 'C_CATEGORY': 'HUMAN', 'C_DESC': 'GUINEA PIG'}]

  Concerning

  Etbin

• ORA-54017: excluded from the regime of virtual columns UPDATE Operation

  Referenced to

  ORA-54017: excluded from the regime of virtual columns UPDATE Operation

  There are problems with v4.0_4.121.1.0 knew?

  Thank you

  Sorry, but after setting StoreGeneratedPattern to Computed in the EF model I have the same problem.

  Thank you

• Unable to create a table with virtual columns... Get the error ORA-12899... Suggestions please.

  Hi all

  Here is the create table script, which does not work, error ORA-12899 keep expressing. Please suggest...,.,.

  CREATE TABLE FX_TRANS
  (
  SAGE_TRADE_TYPE VARCHAR2 (50 BYTE),
  UPSTREAM_EXECUTION_TS TIMESTAMP (9).
  LOCAL_TZ VARCHAR2 (20 BYTE),
  GMT_CONV_ENTERED_DT_TS TIMESTAMP (9) ALWAYS GENERATED IN THE FORM ("SONARDBO". "FN_CONVERT_TIMEZONE"("LOCAL_TZ","ENTERED_DT_TS")), "
  GMT_CONV_EXECUTION_DT_TS TIMESTAMP (9) ALWAYS GENERATED IN THE FORM ("SONARDBO". "FN_CONVERT_TIMEZONE"("LOCAL_TZ","UPSTREAM_EXECUTION_TS")), "
  );

  [Error] Running (5:3): ORA-12899: value too large for column 'GMT_CONV_EXECUTION_DT_TS' (actual: 11, maximum: 20)

  [Error] Performance (6:3): ORA-12899: value too large for column 'GMT_CONV_EXECUTION_DT_TS' (actual: 11, maximum: 20)

  
  Used fucntion Script that I use as a VIRTUAL column expression:

  CREATE OR REPLACE FUNCTION SONARDBO. FN_CONVERT_TIMEZONE
  (
  PI_LOCAL_TZ IN VARCHAR2,
  PI_DT IN TIMESTAMP
  )
  RETURNS THE TIMESTAMP
  DETERMINISTIC
  IS
  LV_TIMESTAMP TIMESTAMP;
  BEGIN
  LV_TIMESTAMP: = CASE WHEN PI_LOCAL_TZ = 'SERGEANT' THEN
  TO_TIMESTAMP (TO_CHAR)
  ((FROM_TZ)
  PI_DT,
  "Asia/Singapore")
  IN THE ZONE IS "GMT"),.
  'YYYY-MM-DD HH. FF H '),'YYYY-MM-DD HH. TZDS FF PM ")"
  WHEN PI_LOCAL_TZ = "GMT" THEN
  TO_TIMESTAMP (TO_CHAR)
  ((FROM_TZ)
  PI_DT,
  "GMT")
  IN THE ZONE IS "GMT"),.
  'YYYY-MM-DD HH. FF H '),'YYYY-MM-DD HH. TZDS FF PM ")"
  WHEN PI_LOCAL_TZ = "IS" THEN
  TO_TIMESTAMP (TO_CHAR)
  ((FROM_TZ)
  PI_DT,
  "America/New_York")
  IN THE ZONE IS "GMT"),.
  'YYYY-MM-DD HH. FF H '),'YYYY-MM-DD HH. TZDS FF PM ")"
  ANOTHER NULL
  END;

  
  RETURN LV_TIMESTAMP;
  EXCEPTION
  WHILE OTHERS THEN
  LIFT;
  END;
  /

  Thank you very much

  Arpit

  This one worked for me.

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

  drop table FX_TRANS;
  
  CREATE TABLE FX_TRANS (
     SAGE_TRADE_TYPE VARCHAR2 (50 BYTE),
     UPSTREAM_EXECUTION_TS TIMESTAMP (9),
     LOCAL_TZ VARCHAR2 (20 BYTE),
     ENTERED_DT_TS TIMESTAMP (9),
     GMT_CONV_ENTERED_DT_TS timestamp(9)
           GENERATED ALWAYS AS
              (cast ("FN_CONVERT_TIMEZONE" ("LOCAL_TZ", "ENTERED_DT_TS") as timestamp(9))),
     GMT_CONV_EXECUTION_DT_TS timestamp(9)
           GENERATED ALWAYS AS
              (cast("FN_CONVERT_TIMEZONE" ("LOCAL_TZ", "UPSTREAM_EXECUTION_TS") as timestamp(9))));
  
  INSERT INTO fx_trans (SAGE_TRADE_TYPE,
                        UPSTREAM_EXECUTION_TS,
                        LOCAL_TZ,
                        ENTERED_DT_TS)
       VALUES ('A',
               SYSTIMESTAMP,
               'SGT',
               SYSTIMESTAMP + 1 / 24);
  
  commit;
  

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

  See you soon,.

  Manik.

• I want to change the table with the expression of dangerousness of the virtual columns with her, need advice

  Hi all

  Here is the structure of the table with two expression of virtual columns associated highlighted, now I want to delete these expressions with virtual columns (but must keep my VIRTUAL columns as it is).

  Is it possible the alter or I need to raise the table, make a new structure and copy content back to newly structured table... Pleae help!

  CREATE TABLE TEST_COL)

  SAGE_TRADE_TYPE VARCHAR2 (50 BYTE),

  LOCAL_TZ VARCHAR2 (20 BYTE),

  ACE GMT_CONV_ENTERED_DT_TS (SAGEDBO. FN_CONVERT_TIMEZONE (LOCAL_TZ, ENTERED_DT_TS)) VIRTUAL,.

  ACE GMT_CONV_EXECUTION_DT_TS (SAGEDBO. FN_CONVERT_TIMEZONE (LOCAL_TZ, UPSTREAM_EXECUTION_TS)) VIRTUAL,.

  EOD_IND VARCHAR2 (10 BYTE)

  );

  Thank you very much

  Arpit

  Try this

  ALTER table test_col change gmt_conv_entered_dt_ts (0) virtual;

  ALTER table test_col change gmt_conv_execution_dt_ts (1) virtual;

• Function index and virtual columns

  I just read the documentation of Oracle on the FBI. In the context of optimization with a function-based index, it is said that "a virtual column is useful for speed of access to data from expressions.". Here is the link Index-Organized Tables and indexes.

  My question is, does Oracle already not create a virtual column when we create a function-based index?

  Concerning

  Charlie

  Hi Charlie
  Yes, the database engine creates a virtual column. But this column is hidden. Reproduced in 11.2.0.3 example:

  SQL> CREATE TABLE t (n NUMBER);SQL> CREATE INDEX i ON t (round(n,0));
  SQL> SELECT column_name, hidden_column, virtual_column  2  FROM user_tab_cols
    3  WHERE table_name = 'T';
  
  COLUMN_NAME                    HIDDEN VIR
  ------------------------------ ------ ---
  N                              NO    NO
  SYS_NC00002$                  YES    YES
  

  HTH

  Chris Antognini

  Troubleshooting performance Oracle, Apress 2008/2014

• ORA-00936: missing expression when adding virtual column

  I am having this error when you add virtual column am in database 11 g

  having error

  ORA-00936: lack of expression

  in select superior

  My sql is

  Employees ALTER TABLE ADD (user name (select upper (substr (first_name, 1, 1)) | initcap (last_name) user name of employees));

  http://docs.Oracle.com/CD/E11882_01/server.112/e41084/statements_3001.htm#sthref3374

  Adding a column of Table virtual: example, the following statement adds a copy of the hr.employees table a column named income , which is a combination of salary more commission. Wages and the commission are NUMBER columns, so the database creates the virtual column as a NUMBER same column if the data type is not specified in the statement:

  CREATE TABLE emp2 AS SELECT * FROM employees; ALTER TABLE emp2 ADD (income AS (salary + (salary*commission_pct)));
  

  ALTER TABLE ADD employees (AS username (upper (substr (first_name, 1, 1)) | initcap (last_name)));

  Concerning

  Etbin

• Adding a virtual column derived from sdo_geometry?

  Hi guys - maybe just a quick: do I do specifically to add a virtual as column the based on a geometry object?

  SQL> select *
    2    from v$version;
  
  
  BANNER
  --------------------------------------------------------------------------------
  Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
  PL/SQL Release 11.2.0.3.0 - Production
  CORE    11.2.0.3.0      Production
  TNS for Linux: Version 11.2.0.3.0 - Production
  NLSRTL Version 11.2.0.3.0 - Production
  
  
  5 rows selected.
  
  
  SQL> create table foo (id number
    2                   ,locn mdsys.sdo_geometry);
  
  
  Table created.
  
  
  SQL>
  SQL> alter table foo add (x number as (locn.sdo_point.x));
  alter table foo add (x number as (locn.sdo_point.x))
                                    *
  ERROR at line 1:
  ORA-54016: Invalid column expression was specified
  
  

  I know that in a query, the table must be qualified with an alias as below:

  don't know how to apply this to a virtual column.

  
  

  SQL> insert into foo values (1,MDSYS.SDO_GEOMETRY(2001,8307,MDSYS.SDO_POINT_TYPE(151.213376,-33.865623,NULL),NULL,NULL));
  
  
  1 row created.
  
  
  SQL> select *
    2    from
    3
  SQL>
  SQL>
  SQL> select f.locn.sdo_point.x
    2    from foo f;
  
  
  LOCN.SDO_POINT.X
  ----------------
        151.213376
  
  
  1 row selected.
  
  
  SQL>
  
  

  
  

  Edit: what should we do to make the display in a fixed rate code in shape with a police?
  

  For me it works with a user defined function:

  SQL> select * from v$version;
  
  BANNER
  --------------------------------------------------------------------------------
  Oracle Database 11g Express Edition Release 11.2.0.2.0 - Production
  PL/SQL Release 11.2.0.2.0 - Production
  CORE    11.2.0.2.0    Production
  TNS for 32-bit Windows: Version 11.2.0.2.0 - Production
  NLSRTL Version 11.2.0.2.0 - Production    
  
  SQL> create table foo (id number
    2                      ,locn mdsys.sdo_geometry);
  
  Table created.
  
  SQL> insert into foo (id, locn) values (1,MDSYS.SDO_GEOMETRY(2001,8307,MDSYS.SDO_POINT_TYPE(151.213376,-33.865623,NULL),NULL,NULL));
  
  1 row created.
  
  SQL> create or replace function get_geometry_x (g mdsys.sdo_geometry) return number deterministic as
    2  begin
    3  return g.sdo_point.x;
    4  end;
    5  /
  
  Function created.
  
  SQL> alter table foo add (x number as (get_geometry_x(locn)));
  
  Table altered.
  
  SQL> select x from foo;
  
           X
  ----------
  151,213376
  

  Message geändert durch hm

• details of the virtual columns and deterministic function

  Hello

  First time that I post a question after the migration of the Forums. So please excuse me if you see errors in format.

  Below, I have created a function as deterministic and a table with a virtual column (column refers to the function)

  Here are my questions

  (1) if I run SELECT * FROM t whenever Oracle will perform the function add_fn?

  (2) what is the advantage of DETERMINISTIC? (Documentation says that if we declare a function as deterministic he will attempt to use previously caluculated results for the same set of values. So, when I ever I run SELECT * FROM t oracle executes add_fn only once and it will use the result for the next time. Is my understanding correct.)

  Here's the code.

  SQL> create or replace function add_fn ( p_n1 in number
    2                                                   ,p_n2 in number )
    3  return number deterministic
    4  is
    5  begin
    6      return p_n1+p_n2;
    7  end;
    8  /
  Function created
  SQL> create table t ( n1 number
    2                       ,n2 number
    3         ,n3 number generated always as (add_fn(n1,n2)) virtual
    4         );
  Table created
  SQL> insert into t (n1,n2) values (10,20);
  1 row inserted
  SQL> select * from t;
          N1         N2         N3
  ---------- ---------- ----------
          10         20         30
  SQL> select * from t;
          N1         N2         N3
  ---------- ---------- ----------
          10         20         30
  SQL>
  

  Hello

  ...
  (1) if I run SELECT * FROM t whenever Oracle will perform the function add_fn?

  (2) what is the advantage of DETERMINISTIC? (Documentation says that if we declare a function as deterministic he will attempt to use previously caluculated results for the same set of values. So, when I ever I run SELECT * FROM t oracle executes add_fn only once and it will use the result for the next time. Is my understanding correct.)

  ...

  (1) oracle will have to evaluate the function.  Because only deterministic functions are allowed, this means that it will not necessarily perform the function again; He can get the value cached from a previous call.

  I think that the indexed values are actually stored in the index.  "SELECT * FROM t;" do not use an index, but if you make another request, then you should be able to get the value of the virtual table of the index, without calling the function or obtaining the value of a cache.

  (2) If a function is DETERMINISTIC, the optimizer may decide whether to actually call the function each time, or the cache for better performance results.  There is no guarantee that it will always be one or the other.  Replace "will be" in your description "may", and then what you say is correct.

• How to remove a virtual column in a table

  Is it possible to delete a virtual column in a table. Please give the full syntax for help do

  What do you mean delete?

  You can do DML on virtual columns because they do not exist. They are virtual...

  You can drop

  alter table table_name drop column column_name;
  

• What is a virtual column...?

  What is a virtual column...?
  can someone explain in brief...

  It is introduced in Oracle 11 g as a new feature of Oracle.

  You can check the link for more information:
  http://docs.Oracle.com/CD/E11882_01/server.112/e17118/statements_7002.htm#BABIJABG