What's the difference beetwen BLOB and CLOB on DB2/400 ?
This data has the same Length ( 1 through 2 147 483 647 )
Thank's
CLOB = Character Large Object
BLOB = Binary Large Object
Characters can be translated between CCSIDs, binary data will not be.
If you're dealing with character data, XML, JSON, plain text, use a CLOB.
If you're dealing with binary data, .ZIP .PDF, then use a BLOB.
Example, you store a CCSID 37 (EBCDIC US ENGLISH) CLOB and retrieve it via JDBC. The data will be translated to unicode by the JDBC driver. The hexadecimal representation of the data will be different.
Same data as a BLOB will be returned unchanged, hexadecimal representation will be unchanged on both sides.
Related
There is one aspect of the extended data types introduced with Oracle 12 that I don't quite understand. The documentation (https://docs.oracle.com/database/121/SQLRF/sql_elements001.htm#SQLRF55623) says:
A VARCHAR2 or NVARCHAR2 data type with a declared size of greater than 4000 bytes, or a RAW data type with a declared size of greater than 2000 bytes, is an extended data type. Extended data type columns are stored out-of-line, leveraging Oracle's LOB technology.
According to this definition does "VARCHAR2(4000 CHAR)" have "a declared size of greater than 4000 bytes" because with a multi-byte character set (e.g. ALS32UTF8) it could contain more that 4000 bytes?
Or more specific: What happens when I create a column of that type? I could think of the following possibilities:
It is created with an extended data type, so that the content of that column is always stored in a CLOB regardless of its size.
The values for that column are stored inline if they need not more than 4000 bytes, and as CLOB if they are longer.
It will refuse to store any values with more than 4000 bytes. To circumvent that I have to declare the column as VARCHAR2(4001 CHAR) or something similar.
Edit: The question had been marked as a duplicate of Enter large content to oracle database for a few weeks, but I don't think it is. The other question is generally about how you can enter more than 4000 characters in a VARCHAR2 column, but I am asking a very specific question about an edge case.
I need to retrieve a CLOB field from oracle db
I have no problems to retrieve first n charachters (using DBMS_LOB.SUBSTR in a query works with limit to 4000 chars), but don't work if I try to retrieve largest field containing unicode chars (kanji).
Is there a method to do so?
I have a database with the below NLS settings
NLS_NCHAR_CHARACTERSET - AL16UTF16
NLS_CHARACTERSET - AL32UTF8
There's a table with a clob column storing a base64 encoded data.
Since the characters are mostly english and letters, I would assume each character takes up 1 byte only as clob using the charset of NLS_CHARACTERSET for encoding.
With a inline enabled clob column, the clob will be stored inline unless it goes more that 4096 bytes in size. However, when I tried to store a set of data with 2048 chars, I found that it is not stored inline (By checking the table DBA_TABLES). So does it mean each character is not using only 1 byte? Can anyone elaborate on this?
Another test added:
Create a table with clob column with chunk size 8kb so that initial segment size is 65536 bytes.
After insert a row with 32,768 chars in clob column. The 2nd extent creation can be told by querying dba_segments.
http://docs.oracle.com/cd/E11882_01/server.112/e10729/ch6unicode.htm#r2c1-t12
It says:
Data in CLOB columns is stored in a format that is compatible with
UCS-2 when the database character set is multibyte, such as UTF8 or
AL32UTF8. This means that the storage space required for an English
document doubles when the data is converted
So it looks like CLOB internally stores everything as UCS-2 (Unicode), i.e. 2 bytes fixed per symbol. Consequently, it stores inline 4096/2 = 2048 chars.
I'm using DBIx::Class to fetch data from Oracle (11.2). when the data fetched, for example "Alfred Kärcher" its returns the value as "Alfred Karcher". I tried to add the $ENV NLS_LANG and NLS_NCHAR but still no change.
I also used the utf8 module to verify that the data is utf8 encoded.
This looks like the Oracle client library converting the data.
Make sure the database encoding is set to AL32UTF8 and the environment variable NLS_LANG to AMERICAN_AMERICA.AL32UTF8.
It might also be possible by setting the ora_(n)charset parameter instead.
The two links from DavidEG contain all the info that's needed to make it work.
You don't need use utf8; in your script but make sure you set STDOUT to UTF-8 encoding: use encoding 'utf8';
here the problem is with the column data type that you specified for the storing
you column database specified as VARCHAR2(10), then for oracle, actually stores the 10 bytes, for English 10 bytes means 10 characters, but in case the data you insert into the column contains some special characters like umlaut, it require 2 bytes. then you end up RA-12899: VALUE too large FOR column.
so in case the data that you inserting into the column which is provided the user and from different countries then use VARCHAR2(10 char)
In bytes: VARCHAR2(10 byte). This will support up to 10 bytes of data, which could be as few as two characters in a multi-byte character sets.
In characters: VARCHAR2(10 char). This will support to up 10 characters of data, which could be as much as 40 bytes of information.
I wish to extract just the first 1024 bytes of a stored blob and not the whole file. The reason for this is I want to just extract the metadata from a file as quickly as possible without having to select the whole blob.
I understand the following:
select dbms_lob.substr(file_blob, 16,1)
from file_upload
where file_upload_id=504;
which returns it as hex. How may I do this so it returns it in binary data without selecting the whole blob?
Thanks in advance.
DBMS_LOB.SUBSTR will, for a BLOB, return a RAW. Most environments will render that in hex.
You can use the DUMP function to view it in some other formats.
select dump(dbms_lob.substr(product_image,10,1),10),
dump(dbms_lob.substr(product_image,10,1),16),
dump(dbms_lob.substr(product_image,10,1),17)
from APEX_DEMO.DEMO_PRODUCT_INFO
where product_id = 9;
This returns the first 10 bytes of the BLOB in decimal (eg 0-255), hex and character. The latter may throw some unprintable garbage to the screen and, if the client and database character sets do not match, undergo some 'translation'.
You can use UTL_RAW.CAST_TO_VARCHAR2 which may give you what you want.
select utl_raw.cast_to_varchar2(dbms_lob.substr(product_image,10,1)) chr
from APEX_DEMO.DEMO_PRODUCT_INFO
where product_id = 9