Is there a length limit (like the infamous 4000 byte) for the resulting concatenation with
'a' || 'b' || ...
and
concat(concat(concat ('a', 'b'), 'c'), ...)
thanks
Google is your friend - use it. The art is always in choosing the proper phrase to search on; maybe "Oracle concatenation operator" would work. You should see what the Oracle documentation says about your question. In short:
If you concatenate many single-character strings like you are, then yes, you will run into the 4000 byte limit for VARCHAR2.
If you want to exceed it, you must enclose at least one of the single-character strings within TO_CLOB() (or cast it to CLOB in some other way). Then there will be no limit to the number of bytes (NOTE: as you said, it is not CHARACTERS but BYTES - some people forget that) but, of course, the result will be a CLOB. There are many things you can do with VARCHAR2 that you can't do with CLOB (you can't join on CLOB values, you can't group or order by a CLOB expression, etc.)
Related
Have existing table called temptable, column largenumber is a NUMBER field, with no precision set:
largenumber NUMBER;
Query:
select largenumber from temptable;
It returns:
-51524845525550100000000000000000000
But If I do
column largenumber format 999999999999999999999999999999999999999
And then
select largenumber from temptable;
It returns:
-51524845525550:100000000000000000000
Why is there a colon?
To test, I took the number, remove the colon, and insert it to another table temptable2, and did the same column largenumber format, the select returns the number without the colon:
select largenumber from temptable2;
It returns:
-51524845525550100000000000000000000
So the colon is not present here.
So what could possibly be in the original number field to cause that colon?
In the original row, If I do a select and try to do any TO_CHAR, REPLACE, CAST, or concatenate to text, it would give me number conversion error.
For example, trying to generate a csv:
select '"' || largenumber || '",'
FROM temptable;
would result in:
ORA-01722 ("invalid number") error occurs when an attempt is made to convert a character string into a number, and the string cannot be converted into a valid number
In a comment (in response to a question from me), you shared that dump(largenumber) on the offending value returns
Typ=2 Len=8: 45,50,56,53,52,48,46,48
From the outset, that means that the data stored on disk is invalid (it is not a valid representation of a value of number data type). Typ=2 is correct, that is for data type number. The length (8 bytes) is correct (we can all count to eight to see that).
What is wrong is the bytes themselves. And, we only need to inspect the first and the last byte to see that.
The first byte is 45. It encodes the sign and the exponent of your number. The first bit (1 or 0) represents the sign: 1 for positive, 0 for negative. 45 is less than 128, so the first bit in the first byte is 0; so the number is negative. (So far this matches what you know about the intended value.)
But, for negative numbers, the last byte is always the magic value 102. Always. In another comment under your original question, Connor McDonald asks about your platform - but this is platform-independent, it is how Oracle encodes numbers for permanent storage on any platform. So, we already know that the dump value you got tells us the value is invalid.
In fact, Connor, in the same comment, gave the correct representation of that number (according to Oracle's scheme for internal representation of numbers). Indeed, just the last byte is wrong: your dump shows 48, but it should be 102.
How can you fix this? If it's a one-off, just use an update statement to replace the value with the correct one and move on. If your table has a primary key, let's call it id, then find the id for this row, and then
update {your_table} set largenumber = -50...... where id = {that_id};
Question is, how many such corrupt values might you have in your table? If it's just one, you can shrug it off; but if it's many (or even "a handful") you may want to figure out how they got there in the first place.
In most cases, the database will reject invalid values; you can't simply insert 'abc' in a number column, for example. But there are ways to get bad data in; even intentionally, and in a repeatable way. So, you would have to investigate how the bad values were inserted (what process was used for insertion).
For a trivial way to insert bad data in a number column, in a repeatable manner, you can see this thread on the Oracle developers forum: https://community.oracle.com/tech/developers/discussion/3903746/detecting-invalid-values-in-the-db
Please be advised that I had just started learning Oracle at that time (I was less than two months in), so I may have said some stupid things in that thread; but the method to insert bad data is described there in full detail, and it was tested. That shows just one possible (and plausible!) way to insert invalid stuff in a table; how it happened in your specific case, you will have to investigate yourself.
Can someone explain why Oracle made the ora-archive-state column a varchar2 of 4000 chars? When using the in-database archiving feature of Oracle 12c, when the column is 0, the record is visible. When anything other than 0, the record is hidden.
What's the purpose of having the extra 3999 chars when simply setting the column to 1 accomplishes the goal? I'm doubting Oracle is just wasting the space.
Because it allows you to mark "archived" rows differently: you can update ORA_ARCHIVE_STATE to different values, for example: to_char(systimestamp,'yyyy-mm-dd hh24:mi:ssxff')
to set it to the date of archiving. And later you can analyze archived records by this column.
I'm doubting Oracle is just wasting the space.
Varchar2 doesn't waste space. It is variable-length character string. Ie varchar2(4000b) doesn't mean it will use 4000 bytes, or varchar2(4000c) ~ chars. That's just maximum allowed column length
I am using N function to update NClob in SQL Query. However, the update using N function is not allowing me to update more than 1900 characters. After removing N function. I am able to update the more than 1900 characters to my NClob column.
Can anyone help me as to why I am not able to update the NClob column using N function? Is there any restriction on it?
Code is
StringBuilder updateQuery = new StringBuilder("update table_name set column_name =");
updateQuery.append(" = N'").append(NClobContent).append("'").append(" , ");
ps.execute(updateQuery.toString());
As stated in the documentation:
A text literal can have a maximum length of 4000 bytes.
The N means the literal is using the national character set, which will be either UTF8 or AL16UTF16 (the latter by default), so even if your long string has fewer then 4000 characters, it can still have more then 4000 bytes.
Without the N the string is interpreted in the database character set, and the literal is then converted to the nation character set as it is stored in your NCLOB. You can therefore potentially have a longer string - if your database character set is single-byte then you could ave up to 4000 characters, though any multibyte characters in your NClobCOntent variable would be corrupted.
Rather than using the N syntax, pass your variable to the database as a stream; you might find this answer a useful starting point. Or you might be able to use this approach, depending on the string length.
Can anyone tell me how to compare column which has clob datatype in oracle for multiple values?
For one value we are comparing like
dbms_lob.compare(attr_value,'A')=0
Similarly if I want to know whether attr_value is in ('A','B','C','D'). I tried this:
dbms_lob.compare(attr_value,'A')=0 or dbms_lob.compare(attr_value,'B')=0 or ...
This is not giving me proper result. Is there any other way?
OR should work fine. Also you may try this:
SELECT * FROM your_tab WHERE CAST(s as VARCHAR2(2)) IN ('A', 'B', 'C', 'D');
but I'm not sure about the performance.
Since it seems you don't really want to compare CLOBS of massive size with a bunch of other massive CLOBS, the fastest way would be to just compare a Substring of the CLOB:
WHERE DBMS_LOB.SUBSTR( attr_value, 4000, 1 ) IN ('A','B','C')
Here 4000 can be replaced by the maximum length of all you comparison values.
If you really want to compare massive CLOBS I don't think a select is the right approach, you
should probably rework your application logic...
DBMS_LOB.COMPARE does an exact comparison between two LOB objects. The documentation says:
COMPARE returns zero if the data exactly matches over the range
specified by the offset and amount parameters. Otherwise, a nonzero
INTEGER is returned.
On Oracle 11g, you could use REGEXP_INSTR function:
SELECT REGEXP_INTR(attr_value,'A|B|C|D|E') from dual;
I hope it helps.
I'm trying to find an efficient, generic way to convert from string to a number in PL/SQL, where the local setting for NLS_NUMERIC_CHARACTERS settings is inpredictable -- and preferable I won't touch it. The input format is the programming standard "123.456789", but with an unknown number of digits on each side of the decimal point.
select to_number('123.456789') from dual;
-- only works if nls_numeric_characters is '.,'
select to_number('123.456789', '99999.9999999999') from dual;
-- only works if the number of digits in the format is large enough
-- but I don't want to guess...
to_number accepts a 3rd parameter but in that case you to specify a second parameter too, and there is no format spec for "default"...
select to_number('123.456789', null, 'nls_numeric_characters=''.,''') from dual;
-- returns null
select to_number('123.456789', '99999D9999999999', 'nls_numeric_characters=''.,''') from dual;
-- "works" with the same caveat as (2), so it's rather pointless...
There is another way using PL/SQL:
CREATE OR REPLACE
FUNCTION STRING2NUMBER (p_string varchar2) RETURN NUMBER
IS
v_decimal char;
BEGIN
SELECT substr(VALUE, 1, 1)
INTO v_decimal
FROM NLS_SESSION_PARAMETERS
WHERE PARAMETER = 'NLS_NUMERIC_CHARACTERS';
return to_number(replace(p_string, '.', v_decimal));
END;
/
select string2number('123.456789') from dual;
which does exactly what I want, but it doesn't seem efficient if you do it many, many times in a query. You cannot cache the value of v_decimal (fetch once and store in a package variable) because it doesn't know if you change your session value for NLS_NUMERIC_CHARACTERS, and then it would break, again.
Am I overlooking something? Or am I worrying too much, and Oracle does this a lot more efficient then I'd give it credit for?
The following should work:
SELECT to_number(:x,
translate(:x, '012345678-+', '999999999SS'),
'nls_numeric_characters=''.,''')
FROM dual;
It will build the correct second argument 999.999999 with the efficient translate so you don't have to know how many digits there are beforehand. It will work with all supported Oracle number format (up to 62 significant digits apparently in 10.2.0.3).
Interestingly, if you have a really big string the simple to_number(:x) will work whereas this method will fail.
Edit: support for negative numbers thanks to sOliver.
If you are doing a lot of work per session, an option may be to use
ALTER SESSION SET NLS_NUMERIC_CHARACTERS = '.,'
at the beginning of your task.
Of course, if lots of other code is executed in the same session, you may get funky results :-)
However we are able to use this method in our data load procedures, since we have dedicated programs with their own connection pools for loading the data.
Sorry, I noticed later that your question was for the other way round. Nevertheless it's noteworthy that for the opposite direction there is an easy solution:
A bit late, but today I noticed the special format masks 'TM9' and 'TME' which are described as "the text minimum number format model returns (in decimal output) the smallest number of characters possible." on https://docs.oracle.com/cloud/latest/db112/SQLRF/sql_elements004.htm#SQLRF00210.
It seems as if TM9 was invented just to solve this particular problem:
select to_char(1234.5678, 'TM9', 'NLS_NUMERIC_CHARACTERS=''.,''') from dual;
The result is '1234.5678' with no leading or trailing blanks, and a decimal POINT despite my environ containing NLS_LANG=GERMAN_GERMANY.WE8MSWIN1252, which would normally cause a decimal COMMA.
select to_number(replace(:X,'.',to_char(0,'fmd'))) from dual;
btw
select to_number(replace('1.2345e-6','.',to_char(0,'fmd'))) from dual;
and if you want more strict
select to_number(translate(:X,to_char(0,'fmd')||'.','.'||to_char(0,'fmd'))) from dual;
Is it realistic that the number of digits is unlimited?
If we assume it is then isn't it a good reason to look into the requirements more carefully?
If we have that fantastic situation when the initial string is super long, then the following does the trick:
select
to_number(
'11111111.2222'
, 'FM' || lpad('9', 32, '9') || 'D' || lpad('9', 30, '9')
, 'NLS_NUMERIC_CHARACTERS=''.,'''
)
from
dual