When I create a table with a CLOB in it, the CLOB column is reported to have a DATA_LENGTH of 4000:
create table test (
data clob
);
-- Returns 4000
select data_length from all_tab_cols
where table_name = 'TEST';
How can I interpret that? Is that some backwards-compatible tweak, considering that the limit for VARCHAR2 is also 4000? Or is this to indicate that I can only insert / update string literals of length 4000? Is this behaviour of SYS.ALL_TAB_COLS documented somewhere?
Up to 4000 bytes can be stored in-line in the tablespace. If the length of the CLOB exceeds 4000 bytes it must be stored in/readed from LOB storage area via special functions.
See also:
http://www.dba-oracle.com/t_blob.htm
http://www.dba-oracle.com/t_table_blob_lob_storage.htm
Related
for using it as a returning type in a function, I need to create a type at database level.
I do it by typing the command :
CREATE TYPE empno_tbl
IS TABLE OF VARCHAR2(100);
but this obliges me to choose a length.
I would like to create a string kind table type without a specific length.
is there a way to do this ?
If you really want it without a length then use CLOB.
CREATE TYPE empno_tbl IS TABLE OF CLOB;
(There is a limit but in Oracle 19c the CLOB datatype has a limit of 4GB * DB_BLOCK_SIZE initialization parameter, which gives a total size of 8 TB to 128 TB, and if you are reaching that limit then there is probably something wrong with your approach.)
The maximum size for a VARCHAR2 is 4000 bytes, so if you can cope with that limit then just use:
CREATE TYPE empno_tbl IS TABLE OF VARCHAR2(4000);
I have stored function which is returning Varchar2 (32767) and I want to use it in select statement under IN But it gives me error when i use it in Select under IN clause.
SELECT * FROM testcustomers1 where no_of_bu1 in(select myMaxLenFunc('test') from dual);
It gives me error
Error :-
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
If the return value is less than 4k it works fine but if it is greater than that it throws the above error.
Please suggest me if I use varchar2 table or Varchar2 are return in stored function how can i use it IN clause in select.
You have the right idea using a collection instead of a string in the IN clause. Then you will not run into this problem. Try something like this:
CREATE OR REPLACE TYPE strings_t IS TABLE OF VARCHAR2 (4000)
/
CREATE OR REPLACE FUNCTION strings
RETURN strings_t
AUTHID DEFINER
IS
BEGIN
RETURN strings_t ('abc', 'def', '123');
END;
/
CREATE TABLE t (s VARCHAR2 (100))
/
BEGIN
INSERT INTO t
VALUES ('abd');
INSERT INTO t
VALUES ('def');
INSERT INTO t
VALUES ('456');
COMMIT;
END;
/
SELECT *
FROM t
WHERE t.s IN (SELECT COLUMN_VALUE FROM TABLE (strings ()))
/
Your function is PL/SQL and can return a varchar2 string of more than 4000. This is illegal for SQL (if the MAX_STRING_SIZE parameter is of value STANDARD)
http://docs.oracle.com/cd/E11882_01/appdev.112/e17126/datatypes.htm
VARCHAR2 Maximum Size in PL/SQL: 32,767 bytes Maximum Size in SQL
4,000 bytes
So you need to find a way around. Since no_of_bu1 is a SQL column and cannot have more than 4000 bytes in content length you are save with this:
SELECT * FROM testcustomers1
where no_of_bu1 in(select substr(myMaxLenFunc('test'),1,4000) from dual);
Although I would truncate the string within the function.
If your DB is of Oracle 12.1 you can find out if your are STANDARD in SQL stringsize (i.e. 4000)
SELECT name, value
FROM v$parameter
WHERE name = 'max_string_size'
I want to reverse clob data type value in oracle in same way as we do for string data type fields with the help of 'reverse' function.Is there any inbuilt method for that.Google was not much help.Being a newbie in sql don't know whether it is even possible? I initially thought
that 'reverse' function can be used for clob data type fields also but its not working, here is the example I have tried-
drop table test;
create table test
(
name varchar2(4000),
description clob
)
insert into test values ('aadinath','I have to reverse a clob data type value')
select reverse(name) from test;
output= htanidaa
select reverse(name), reverse(description) from test;
output= ORA-00932: inconsistent datatypes: expected CHAR got CLOB
00932. 00000 - "inconsistent datatypes: expected %s got %s"
You need to convert clob to varchar2 first. Then perform the reverse.
Reference 1:
The Function to translate CLOB datatype into varchar() is DBMS_LOB. The DBMS_LOB package provides subprograms to operate on BLOBs, CLOBs, NCLOBs, BFILEs, and temporary LOBs. You can use DBMS_LOB to access and manipulation specific parts of a LOB or complete LOBs. DBMS_LOB can read and modify BLOBs, CLOBs, and NCLOBs; it provides read-only operations for BFILEs.
Syntax:
DBMS_LOB.SUBSTR (lob_loc, amount, offset)
dbms_lob.substr( clob_column, for_how_many_bytes, from_which_byte );
Parameter Description:
lob_loc: Locator for the LOB to be read i.e CLOB column name.
amount: Number of bytes (for BLOBs) or characters (for CLOBs) to be read.
offset: Offset in bytes (for BLOBs) or characters (for CLOBs) from the start of the LOB.
Example:
CREATE OR REPLACE VIEW temp_view
AS
SELECT
column1, -- datatype numeric
column2, -- datatype varchar()
DBMS_LOB.SUBSTR(column3, 2000,1) as column3, -- datatype CLOB
column4 -- datatype numeric
FROM temp_table;
Note: In this example I am reading first 2000 charactres.
Multi-byte characters had caused me a lot of pain.
Any suggestion for this problem?
I have a CLOB field that might contains some multi-byte characters, and I need to select in SQL and convert this field into a string for downstream process, currently I am using:
SELECT DBMS_LOB.SUBSTR( description, 4000, 1 ) FROM table
But the 4000 in above command is in length of characters, rather than bytes. So I had to change to 3000 to handle any multi-byte characters that might have crept into the data else buffer size error will occur.
The problem is for records that do not contain multibyte character, it might unnecessarily truncated more data than it need to.
(The 4000 is the string limitation, we can/had to live with that.)
Is there a way to do something in equivalent of:
SELECT DBMS_LOB.SUBSTR( description, 4000bytes, 1 ) FROM table
That way I can get as much data out as possible.
Note: I am not allowed to create temp tables/views, not using PL/SQL, only SQL SELECT...
Jeffrey's thinking process is ok, but alchn is also right. Just ran into this same problem and here is my solution. You'll have to be able to create a function though:
Create Or Replace Function clob_substr(p_clob In Clob
,p_offset In Pls_Integer
,p_length In Pls_Integer) Return Varchar2 Is
Begin
Return substrb(dbms_lob.substr(p_clob
,p_length
,p_offset)
,1
,p_length);
End;
/
Here is a demo of it's use:
Select c
,clob_substr(c
,1
,4000)
From (
Select xmlelement("t", rpad('é', 4000, 'é'), rpad('é', 4000, 'é')).extract('//text()').getclobval() c
From dual
);
Maybe truncate the resulting varchar2 with SUBSTR:
SELECT SUBSTRB( DBMS_LOB.SUBSTR( description, 4000, 1 ), 1, 4000) FROM table
I am trying to see from an SQL console what is inside an Oracle BLOB.
I know it contains a somewhat large body of text and I want to just see the text, but the following query only indicates that there is a BLOB in that field:
select BLOB_FIELD from TABLE_WITH_BLOB where ID = '<row id>';
the result I'm getting is not quite what I expected:
BLOB_FIELD
-----------------------
oracle.sql.BLOB#1c4ada9
So what kind of magic incantations can I do to turn the BLOB into it's textual representation?
PS: I am just trying to look at the content of the BLOB from an SQL console (Eclipse Data Tools), not use it in code.
First of all, you may want to store text in CLOB/NCLOB columns instead of BLOB, which is designed for binary data (your query would work with a CLOB, by the way).
The following query will let you see the first 32767 characters (at most) of the text inside the blob, provided all the character sets are compatible (original CS of the text stored in the BLOB, CS of the database used for VARCHAR2) :
select utl_raw.cast_to_varchar2(dbms_lob.substr(BLOB_FIELD)) from TABLE_WITH_BLOB where ID = '<row id>';
SQL Developer provides this functionality too :
Double click the results grid cell, and click edit :
Then on top-right part of the pop up , "View As Text" (You can even see images..)
And that's it!
You can use below SQL to read the BLOB Fields from table.
SELECT DBMS_LOB.SUBSTR(BLOB_FIELD_NAME) FROM TABLE_NAME;
Use this SQL to get the first 2000 chars of the BLOB.
SELECT utl_raw.cast_to_varchar2(dbms_lob.substr(<YOUR_BLOB_FIELD>,2000,1)) FROM <YOUR_TABLE>;
Note: This is because, Oracle will not be able to handle the conversion of BLOB that is more than length 2000.
If you want to search inside the text, rather than view it, this works:
with unzipped_text as (
select
my_id
,utl_compress.lz_uncompress(my_compressed_blob) as my_blob
from my_table
where my_id='MY_ID'
)
select * from unzipped_text
where dbms_lob.instr(my_blob, utl_raw.cast_to_raw('MY_SEARCH_STRING'))>0;
I can get this to work using TO_CLOB (docs):
select
to_clob(BLOB_FIELD)
from
TABLE_WITH_BLOB
where
ID = '<row id>';
This works for me in Oracle 19c, with a BLOB field which larger the the VARCHAR limit. I get readable text (from a JSON-holding BLOB)
Barn's answer worked for me with modification because my column is not compressed. The quick and dirty solution:
select * from my_table
where dbms_lob.instr(my_UNcompressed_blob, utl_raw.cast_to_raw('MY_SEARCH_STRING'))>0;
I struggled with this for a while and implemented the PL/SQL solution, but later realized that in Toad you can simply double click on the results grid cell, and it brings up an editor with contents in text. (i'm on Toad v11)
In case your text is compressed inside the blob using DEFLATE algorithm and it's quite large, you can use this function to read it
CREATE OR REPLACE PACKAGE read_gzipped_entity_package AS
FUNCTION read_entity(entity_id IN VARCHAR2)
RETURN VARCHAR2;
END read_gzipped_entity_package;
/
CREATE OR REPLACE PACKAGE BODY read_gzipped_entity_package IS
FUNCTION read_entity(entity_id IN VARCHAR2) RETURN VARCHAR2
IS
l_blob BLOB;
l_blob_length NUMBER;
l_amount BINARY_INTEGER := 10000; -- must be <= ~32765.
l_offset INTEGER := 1;
l_buffer RAW(20000);
l_text_buffer VARCHAR2(32767);
BEGIN
-- Get uncompressed BLOB
SELECT UTL_COMPRESS.LZ_UNCOMPRESS(COMPRESSED_BLOB_COLUMN_NAME)
INTO l_blob
FROM TABLE_NAME
WHERE ID = entity_id;
-- Figure out how long the BLOB is.
l_blob_length := DBMS_LOB.GETLENGTH(l_blob);
-- We'll loop through the BLOB as many times as necessary to
-- get all its data.
FOR i IN 1..CEIL(l_blob_length/l_amount) LOOP
-- Read in the given chunk of the BLOB.
DBMS_LOB.READ(l_blob
, l_amount
, l_offset
, l_buffer);
-- The DBMS_LOB.READ procedure dictates that its output be RAW.
-- This next procedure converts that RAW data to character data.
l_text_buffer := UTL_RAW.CAST_TO_VARCHAR2(l_buffer);
-- For the next iteration through the BLOB, bump up your offset
-- location (i.e., where you start reading from).
l_offset := l_offset + l_amount;
END LOOP;
RETURN l_text_buffer;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('!ERROR: ' || SUBSTR(SQLERRM,1,247));
END;
END read_gzipped_entity_package;
/
Then run select to get text
SELECT read_gzipped_entity_package.read_entity('entity_id') FROM DUAL;
Hope this will help someone.
You can try this:
SELECT TO_CHAR(dbms_lob.substr(BLOB_FIELD, 3900)) FROM TABLE_WITH_BLOB;
However, It would be limited to 4000 byte
Worked for me,
select lcase((insert(
insert(
insert(
insert(hex(BLOB_FIELD),9,0,'-'),
14,0,'-'),
19,0,'-'),
24,0,'-'))) as FIELD_ID
from TABLE_WITH_BLOB
where ID = 'row id';
Use TO_CHAR function.
select TO_CHAR(BLOB_FIELD) from TABLE_WITH_BLOB where ID = '<row id>'
Converts NCHAR, NVARCHAR2, CLOB, or NCLOB data to the database character set. The value returned is always VARCHAR2.