What is the empty string, the value null in the column, or...?

I use Oracle 11.2, a table tb_class as follows:

TB_CLASS (number (3) id, varchar2 (32) nm, seqNum number (3));

1, 212
2, "under", 12
3, 'qq', 12

Select * from TB_CLASS where id = 1 and n = null;... .no selected line
Select nvl (nm) in the TB_CLASS where id = 1; ... 1 selected line

Any know what's in the column of row id = 1 nm? I thought that it is an empty string, but why it returns no rows in the first query?

Thank you!

(1) in Oracle there is no difference between NULL and an empty string.

(2) NULL is never equal to what whatsoever (including another NULL). NULL is never spotty what whatsoever (including another NULL). You must use the IS NULL and IS NOT NULL operators to search for NULL values

SELECT *
  FROM tb_class
 WHERE nm IS NULL

SELECT *
  FROM tb_class
 WHERE nm IS NOT NULL

Of course, it is also possible that you declare that the NM column contains one or more spaces or it contains one or more non-printable characters and not a NULL value. That's why we asked you what dump (nm) returns

Justin

Tags: Database

Similar Questions

What SYS tables (not seen) contains the value NULL spec /not/ column definition?
What SYS (or tables) store the value of a spec /not/ NULL columns? (It doesn't seem to be COL$)

NOTE: This is NOT a trick question - although it seems to be.

Test configuration:
```
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE     11.2.0.1.0     Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
```
Test configuration:
1. a table is created by SCOTT in the SCOTT schema with a NULLABLE column.

2. a primary key constraint is added using only the NULLABLE column

3. Requests for information on USER_TAB_COLS, ALL_TAB_COLS, DBA_TAB_COLS and SYS. COL$ see NOT NULL for the column NULLABLE
as necessary for a primary key constraint. Views derive their data from the column of $ NULL the sys. Table of $ COL
using
```
'DECODE (SIGN (c.null$), -1, 'D', 0, 'Y', 'N'),
```
and the table of $ COL shows a numerical value of '0' before you add the primary key and a value of "1" later.

4. a query on the DDL metadata table shows the specification for column NULLABLE of origin involved.

Question - where this original specification NULLABLE is stored?

This question is based on a question asked by another user in this thread
Columns becoming nullable after a fall of primary key?

I created the following specially for that matter test case
```
-- scott ensures table does not exist
DROP TABLE tbl_test CASCADE CONSTRAINTS;

-- scott creates a table
CREATE TABLE tbl_test ( col_1 NUMBER,
col_2 NUMBER NOT NULL);

-- scott queries to check the the column nullable status
SELECT table_name, column_name, nullable 
FROM user_tab_cols
WHERE table_name = 'TBL_TEST';

-- TABLE_NAME | COLUMN_NAME | NULLABLE
-- TBL_TEST   | COL_1       | Y 
-- TBL_TEST   | COL_2       | N 

-- Scott addes a primary key constraint using only the nullable column
ALTER TABLE tbl_test ADD CONSTRAINT tbl_test_pk PRIMARY KEY(col_1);

-- scott queries to check the the column nullable status
SELECT table_name, column_name, nullable 
FROM user_tab_cols
WHERE table_name = 'TBL_TEST';

TABLE_NAME,COLUMN_NAME,NULLABLE
TBL_TEST,COL_1,N
TBL_TEST,COL_2,N

-- scott queries to get the table DDL
select dbms_metadata.get_ddl('TABLE', 'TBL_TEST', 'SCOTT') FROM DUAL;

DBMS_METADATA.GET_DDL('TABLE','TBL_TEST','SCOTT')

  CREATE TABLE "SCOTT"."TBL_TEST" 
   (     "COL_1" NUMBER,                   <------ where is this NULLABLE spec stored? 
     "COL_2" NUMBER NOT NULL ENABLE, 
      CONSTRAINT "TBL_TEST_PK" PRIMARY KEY ("COL_1")
  USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS NOCOMPRESS LOGGING
  TABLESPACE "USERS"  ENABLE
   ) SEGMENT CREATION DEFERRED 
  PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
  TABLESPACE "USERS" 
```
The DOF shows that Oracle keeps the original spec NULLABLE for the column and uses it to generate the DDL orginal, even if there is a primary key on the table and the system views (and COL$) show the column non NULLABLE.

So where is the original information NULLABLE actually stored?
rp0428 wrote:
What SYS (or tables) store the value of a spec /not/ NULL columns? (It doesn't seem to be COL$)

I think that it becomes a bit messy depending on order of activity:

You can see Col. .null$ is set to a non-zero when the desrcibe command displays the column as not null, but it can happen for two reasons:
(a) user sets the column as not null - in which case you get a line in cdef$ with type # = 7
(b) the user adds a primary key to table - in which case you get a line in cdef$ with type # = 2

If you declare null AND add a primary key, you get two lines - that's why it is possible for Oracle to determine if he should remove the flag not null when you remove the primary key and also allows dbms_metadata show the create statement of table without a NOT NULL even when describe it the watch with a NOT NULL - dbms_metadata can respond to the presence of the type # = 2 and absence of the type # = 7.

Concerning
Jonathan Lewis

By the way: by a strange coincidence, it seems to me answering the previous post, three days before it was asked: http://jonathanlewis.wordpress.com/2012/04/19/drop-constraint/#comment-46140 (on the doubts, this isn't - it answers a different question on the removal of constraints).

Published by: Jonathan Lewis April 23, 2012 11:07

What is the column location in Thunderbird?

What I * want * it is is the e-mail file is stored in the, when I look at my search, as _All Mail_ or laborious Attachments_ folders. As it is, it seems to * always * be empty. What is it?

When your doing a global search and select the show as a list when the results come back. The folder in which the mail is located appears in this column.

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DB version: 11.2 on Solaris 11
The official documentation V $ ARCHIVED_LOG provides the following information on FIRST_TIME and NEXT_TIME, columns COMPLETION_TIME
http://docs.Oracle.com/CD/E18283_01/server.112/e17110/dynviews_1016.htm
FIRST_TIME-> Timestamp of the first amendment
NEXT_TIME-> Timestamp of the next change
COMPLETION_TIME-> time when archiving complete

NEXT_TIME and COMPLETION_TIME seem to be the same for most of the files. I see FIRST_TIME and NEXT_TIME in V$ LOG as well. So I guess FIRST_TIME is at startup when online entries written LGWR Redo sequence Redolog X.
and NEXT_TIME is the time when LGWR finished writing Redo entries to Redolog sequence X online.
V$ ARCHIVED_LOG.completion_time seems to be the same that NEXT_TIME, so archiving seems to occur as soon as the written LGWR is finished.
My above assumption is correct?
Select name, first_time, next_time, completion_time from v$ archived_log where status = 'A' and rownum < 9
NAME FIRST_TIME NEXT_TIME COMPLETION_TIME
-------------------------------------------------------------------------------- ---------------- ---------------- ----------------
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_2_seq_16832.941.852436253 07/09/2014 02:58 07/09/2014 03:50 07/09/2014 03:51
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_2_seq_16833.940.852439233 07/09/2014 03:50 07/09/2014 04:40 07/09/2014 04:40
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_1_seq_16296.937.852442223 07/09/2014 02:58 07/09/2014 05:30 07/09/2014 05:30
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_2_seq_16834.939.852442221 07/09/2014 04:40 07/09/2014 05:30 07/09/2014 05:30
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_2_seq_16835.936.852444733 07/09/2014 05:30 07/09/2014 06:12 07/09/2014 06:12
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_2_seq_16836.935.852446839 07/09/2014 06:12 07/09/2014 06:47 07/09/2014 06:47
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_2_seq_16837.933.852455413 07/09/2014 06:47 07/09/2014 09:10 07/09/2014 09:10
+CTG_ARCH/ctgsprd/ARCHIVELOG/2014_07_09/thread_1_seq_16297.932.852455415 07/09/2014 05:30 07/09/2014 09:10 07/09/2014 09:10
SQL > fixed lines 80
SQL > Journal of the desc v$
Name                                      Null?    Type
----------------------------------------- -------- ----------------------------
GROUP#                                             NUMBER
THREAD NUMBER #
SEQUENCE NUMBER #.
BYTES                                              NUMBER
NUMBER OF BLOCKSIZE
NUMBER OF MEMBERS
ARCHIVED VARCHAR2 (3)
STATUS VARCHAR2 (16)
FIRST_CHANGE # NUMBER
FIRST_TIME DATE
NEXT_CHANGE # NUMBER
DATE OF NEXT_TIME
SQL >

> Thus, archiving seems to occur as soon as the written LGWR is finished.

Of course. Yes. ARCH resumes when LGWR notifies that he ended up writing in the journal online redo (file) and tipped the next newspaper.

Note: There may be a slight delay between the NEXT_TIME and COMPLETION_TIME when the log file is large and/or writing ARCH is slow.

Hemant K Collette

Empty string and null
Hello

Oracle treats the empty string as a NULL value.
If it is so, can force us db to treat two different things.

Thanx
11 g DBA wrote:
Hello

Oracle treats the empty string as a NULL value.

Yes.

If it is so, can force us db to treat two different things.

N °

Please read in SQL Reference:
http://docs.Oracle.com/CD/E11882_01/server.112/e26088/sql_elements005.htm#SQLRF3003

Error trying to filter the column named 'value' in the tab data
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ORA-01722 invalid number
Code provider 1722

Is there a way I can filter this column? I tried quotes around column name, 'value' = 60, but that did not help.

Thank you
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What is the column data type and details? What happens if you (single) quote "60" instead?

K.

Published by: - K - 10/28/2009 14:12: corrected apostrophes

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12.1.3 JDev is used.
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Displaying a string instead of the "null" value in the columns of answers
Hi, is it possible to display a string (e.g. "no data") in responses instead a NULL value in a column of a table or a PivotTable? I read everything by using the formula in the column section in the answers, but I do not understand what expression should be used... could you help me?

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You must do this in the business model and the Mapping layer

Go to the properties of the column

1. in general tab, you have "use existing columns of logic as a source.
Select this check box. Click the period (...)
In the formula for the column, you can add the condition of ifnull
In this col formula editor, you can choose the logical columns.

2. on the Data Type tab, you have the maps and logical sources
Here too you can achieve.
In this col formula editor, you can choose physical columns.

Kind regards
Rambeau

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```
N/A
```

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Development platform: 32-bit Windows 7, LV2012 Professional Development System.

Production of platforms: Windows XP.

We have a test application, we have developed (in haste, I might add) who has a curious problem. As part of the installation for each test, read us a text box with a serial number entry and record them in the log files. Series enough.

This works very well on production machines - no apparent problem.

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Clear the text box repeatedly, I'm looking to see if any of those that occur at the wrong time. And, indeed, I am looking a probe value of ' ' from the property node Value with the string "1234" visible in the text box while NONE of the compensation functions have been affected.

The test application uses a pretty standard user interface event loop model, with an event loop manages the user input and the other event loop manages the business logic.

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As promised, I did go to the bottom of it.

Simply enable "update of value while typing" gave me the result I expected.

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Greetings, Folks.
It's driving me crazy. I can reproduce the problem over and over again. I'm missing a reason why cell.contents would be assessed differently in the case of condition in excess than no? I don't understand...
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Object in question is a line of 3 cells with values in the respective cells: text, double value, double the value.
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TT

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myCell.texts [0] .silence

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Hi people,

I know it's a long shot, but anyone happen to know what is on line 189 of the MDSYS. SDO_TOPO_MAP? :-)

We are copying valid topologies 10.2.0.4 to 11.2.0.2 using exp/imp, following the standard procedure and also add toid_novalidate to the need:

IMP < user > / < pw > @ < database > FILE = < file > .dmp TOID_NOVALIDATE = MDSYS. SDO_GEOMETRY, MDSYS. SDO_ELEM_INFO_ARRAY, MDSYS. SDO_ORDINATE_ARRAY, MDSYS. Index SDO_TOPO_GEOMETRY = ignore tables N = Y = (< list table >)

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It is a combination of a JDBC bug and a corruption of data due to the bug in 10.2.
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You must correct the sdo_geometry columns in the tables of topology using this procedure and it will work fine after that.

create or replace function id_geom (sdo_geometry g)
deterministic sdo_geometry back as
G1 sdo_geometry;
IDX number;
Sdo_ordinate_array ADR;
x number;
number of y;
number of z;
point_t SDO_POINT;
Start
If (g.sdo_point is not NULL) then
x: = NULL; y: = NULL; z: = NULL;
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x: = g.sdo_point.x * 10;
x: = x / 10.
end if;
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y: = g.sdo_point.y * 10;
y: = y / 10;
end if;
If (g.sdo_point.z is not NULL) then
z: = g.sdo_point.z * 10;
z: = z / 10;
end if;
point_t: = SDO_POINT_TYPE (x, y, z);
on the other
point_t: = NULL;
end if;

If (g.sdo_ordinates is not NULL) then
ADR: = sdo_ordinate_array();
ords.extend (g.sdo_ordinates. (Count);
for idx in 1... loop ords. Count
x: = g.sdo_ordinates (idx);
x: = (x * 10.0);
x: = x / 10.0;
ords (idx): = x;

end loop;
G1: = sdo_geometry (g.sdo_gtype, g.sdo_srid, point_t, g.sdo_elem_info, ords);
on the other
G1: = sdo_geometry (g.sdo_gtype, g.sdo_srid, point_t, g.sdo_elem_info, NULL);
end if;

return g1;
end;
/

so that you can SQL like this to fix the sdo_geometry columns in all the tables in the topology:
Update test_topology_edge$ a set a.geometry = id_goem (geometry);

Make sure that the Spatial index is deleted before doing this operation.

Siva

What is the empty string, the value null in the column, or...?

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