I have a table A with single column
**TableA**
Row1
Row2
Row3
.....
I have to convert the table rows into a list and store them in variables. So that they are stored as
Row1,Row2,Row3,....,Rown
I used the listagg () function to achieve the solution.
DECLARE
tbl_list CLOB;
BEGIN
SELECT listagg (''''||Column_name||'''',',') WITHIN GROUP (ORDER BY Column_name) INTO TBL_LIST FROM TableA;
END;
This works fine if the TableA has few rows. But if the table has lots of rows I get the following error
ORA-01489: result of string concatenation is too long
Is this due to the storage limit of variable TBL_LIST? Can anyone explain me what is wrong. And is there an alternate for lisagg(), to achieve the result, I want?
listagg function is limited to 4000 characters, if it exceeds 4000 character yo may get an error ORA-01489: result of string concatenation is too long
You can use XMLAGG which is not limited to 4000 char.
SELECT
RTRIM(XMLAGG(XMLELEMENT(E,''''||Column_name||'''',',').EXTRACT('//text()')
ORDER BY Column_name).GetClobVal(),',')
from TableA;
you can refer this question: How to tweak LISTAGG to support more than 4000 character in select query?
If you expect the result of aggregation to be more than 4000 bytes? If so, you could potentially create a user-defined aggregate function that returns a CLOB rather than a VARCHAR2. If you don't expect the result to exceed 4000 bytes there is probably something wrong with the way you've specified the aggregate.
Please refer to the "https://oracle-base.com/articles/misc/string-aggregation-techniques" for user defined aggregation.
Related
I have a table with a CLOB column. What I need to do is query the table, and combine the CLOB column of each row into a single CLOB column.
So, say I have something like:
ABC CLOB_VALUE1
ABC CLOB_VALUE2
ABC CLOB_VALUE2
What I need at output is:
ABC Combined Value (CLOB_VALUE1, CLOB_VALUE2, CLOB_VALUE3)
LISTAGG will not work due to the length, and I'm not having any luck with XMLAGG (unless I am doing it wrong).
I tried this, but it is not retrieving all the records:
SELECT id, XMLAGG(XMLELEMENT(E,price_string||',') ORDER BY
price_date).EXTRACT('//text()').getclobval() AS daily_7d_prices
FROM daily_price_coll
WHERE price_date >= TRUNC(SYSDATE) - 7
GROUP BY id;
I'm only getting the most recent row, when there are actually 3 rows in the table.
Any ideas?
I'm facing a problem when I try to use LAG function on CLOB column.
So let's assume we have a table
create table test (
id number primary key,
not_clob varchar2(255),
this_is_clob clob
);
insert into test values (1, 'test1', to_clob('clob1'));
insert into test values (2, 'test2', to_clob('clob2'));
DECLARE
x CLOB := 'C';
BEGIN
FOR i in 1..32767
LOOP
x := x||'C';
END LOOP;
INSERT INTO test(id,not_clob,this_is_clob) values(3,'test3',x);
END;
/
commit;
Now let's do a select using non-clob columns
select id, lag(not_clob) over (order by id) from test;
It works fine as expected, but when I try the same with clob column
select id, lag(this_is_clob) over (order by id) from test;
I get
ORA-00932: inconsistent datatypes: expected - got CLOB
00932. 00000 - "inconsistent datatypes: expected %s got %s"
*Cause:
*Action:
Error at Line: 1 Column: 16
Can you tell me what's the solution of this problem as I couldn't find anything on that.
The documentation says the argument for any analytic function can be any datatype but it seems unrestricted CLOB is not supported.
However, there is a workaround:
select id, lag(dbms_lob.substr(this_is_clob, 4000, 1)) over (order by id)
from test;
This is not the whole CLOB but 4k should be good enough in many cases.
I'm still wondering what is the proper way to overcome the problem
Is upgrading to 12c an option? The problem is nothing to do with CLOB as such, it's the fact that Oracle has a hard limit for strings in SQL of 4000 characters. In 12c we have the option to use extended data types (providing we can persuade our DBAs to turn it on!). Find out more.
Some of the features may not work properly in SQL when using CLOBs(like DISTINCT , ORDER BY GROUP BY etc. Looks like LAG is also one of them but, I couldn't find anywhere in docs.
If your values in the CLOB columns are always less than 4000 characters, you may use TO_CHAR
select id, lag( TO_CHAR(this_is_clob)) over (order by id) from test;
OR
convert it into an equivalent SELF JOIN ( may not be as efficient as LAG )
SELECT a.id,
b.this_is_clob AS lagging
FROM test a
LEFT JOIN test b ON b.id < a.id;
Demo
I know this is an old question, but I think I found an answer which eliminates the need to restrict the CLOB length and wanted to share it. Utilizing CTE and recursive subqueries, we can replicate the lag functionality with CLOB columns.
First, let's take a look at my "original" query:
WITH TEST_TABLE AS
(
SELECT LEVEL ORDER_BY_COL,
TO_CLOB(LEVEL) AS CLOB_COL
FROM DUAL
CONNECT BY LEVEL <= 10
)
SELECT tt.order_by_col,
tt.clob_col,
LAG(tt.clob_col) OVER (ORDER BY tt.order_by_col)
FROM test_table tt;
As expected, I get the following error:
ORA-00932: inconsistent datatypes: expected - got CLOB
Now, lets look at the modified query:
WITH TEST_TABLE AS
(
SELECT LEVEL ORDER_BY_COL,
TO_CLOB(LEVEL) AS CLOB_COL
FROM DUAL
CONNECT BY LEVEL <= 10
),
initial_pull AS
(
SELECT tt.order_by_col,
LAG(tt.order_by_col) OVER (ORDER BY tt.order_by_col) AS PREV_ROW,
tt.clob_col
FROM test_table tt
),
recursive_subquery (order_by_col, prev_row, clob_col, prev_clob_col) AS
(
SELECT ip.order_by_col, ip.prev_row, ip.clob_col, NULL
FROM initial_pull ip
WHERE ip.prev_row IS NULL
UNION ALL
SELECT ip.order_by_col, ip.prev_row, ip.clob_col, rs.clob_col
FROM initial_pull ip
INNER JOIN recursive_subquery rs ON ip.prev_row = rs.order_by_col
)
SELECT rs.order_by_col, rs.clob_col, rs.prev_clob_col
FROM recursive_subquery rs;
So here is how it works.
I create the TEST_TABLE, this really is only for the example as you should already have this table somewhere in your schema.
I create a CTE of the data I want to pull, plus a LAG function on the primary key (or a unique column) in the table partitioned and ordered in the same way I would have in my original query.
Create a recursive subquery using the initial row as the root and descending row by row joining on the lagged column. Returning both the CLOB column from the current row and the CLOB column from its parent row.
I have an issue where a Oracle DB column(say 'REF_NO') is VARCHAR2 and carries values similar to the ones below
If I do an ORDER BY REF_NO I get this:
LET-2-1
LET-2-10
LET-2-11
LET-2-2
LET-2-3
Which makes sense because the values are being treated as characters. I have been asked to change this so that the returned results are ordered like this:
LET-2-1
LET-2-2
LET-2-3
LET-2-10
LET-2-11
I cannot guarantee the format of these values either so I cannot really see how I can use regex or sub-string as it's a completely free text entry for users to enter values. The example above just happens to be what the requested data looks like. Other data could be completely different.
I cannot see how this is possible, so was hoping for some suggestions.
Additional information
To add to the complexity, here are some more examples from other customers:
Customer 1: OB 12, WE-11, WAN-001
Customer 2: P4, D1, W9
Customer 3: NTT-33A, RLC-33L, ARR-129B
Here are the steps
create table test01 (c varchar2(30));
insert into test01 values ('LET-2-1');
insert into test01 values ('LET-2-10');
insert into test01 values ('LET-2-2');
Query
select * from test01
order by to_number(SUBSTR(C,INSTR(C,'-',1)+1,INSTR(C,'-',1,2)-INSTR(C,'-',1)-1)),
to_number(SUBSTR(C,INSTR(C,'-',-1)+1));
Assuming all the values are having structure of -- - in the above query I try to extract numbers and converted to number in order by clause.
select * from TABLE
ORDER BY LENGTH(REF_NO), REF_NO
first you need to order by length and then order by REF_NO
I'm trying to use a nested table inside the IN clause in a PL-SQL block.
First, I have defined a TYPE:
CREATE OR REPLACE TYPE VARCHAR_ARRAY AS TABLE OF VARCHAR2(32767);
Here is my PL-SQL block using the 'BULK COLLECT INTO':
DECLARE
COL1 VARCHAR2(50) := '123456789';
N_TBL VARCHAR_ARRAY := VARCHAR_ARRAY();
C NUMBER;
BEGIN
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('START: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
SELECT COLUMN1
BULK COLLECT INTO N_TBL
FROM MY_TABLE
WHERE COLUMN1 = COL1;
SELECT COUNT(COLUMN1)
INTO C
FROM MY_OTHER_TABLE
WHERE COLUMN1 IN (SELECT column_value FROM TABLE(N_TBL));
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('ENDED: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
END;
And the output is:
START: 01-08-2014 12:36:14.997
ENDED: 01-08-2014 12:36:17.554
It takes more than 2.5 seconds (2.557 seconds exactly)
Now, If I replace the nested table by a subquery, like this:
DECLARE
COL1 VARCHAR2(50) := '123456789';
N_TBL VARCHAR_ARRAY := VARCHAR_ARRAY();
C NUMBER;
BEGIN
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('START: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
SELECT COUNT(COLUMN1)
INTO C
FROM MY_OTHER_TABLE
WHERE COLUMN1 IN (
-- Nested table replaced by a subquery
SELECT COLUMN1
FROM MY_TABLE
WHERE COLUMN1 = COL1
);
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('ENDED: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
END;
The output is:
START: 01-08-2014 12:36:08.889
ENDED: 01-08-2014 12:36:08.903
It takes only 14 milliseconds...!!!
What could I do to enhance this PL-SQL block ?
Is there any database configuration needed?
Are the two query plans different?
Assuming that they are, the difference is likely that the optimizer has reasonable estimates about the number of rows the subquery will return and, thus, is able to choose the most efficient plan. When your data is in a nested table (I'd hate to use the word array in the type declaration here since that implies that you're using a varray when you're not), Oracle doesn't have information about how many elements are going to be in the collection. By default, it's going to guess that the collection has as many elements as your data blocks have bytes. So if you have 8k blocks, Oracle will guess that your collection has 8192 elements.
Assuming that your actual query doesn't return anywhere close to 8192 rows and that it actually returns many more or many fewer rows, you can potentially use the cardinality hint to let the optimizer make a more accurate guess. For example, if your query generally returns a few dozen rows, you probably want something like
SELECT COUNT(COLUMN1)
INTO C
FROM MY_OTHER_TABLE
WHERE COLUMN1 IN (SELECT /*+ cardinality(t 50) */ column_value
FROM TABLE(N_TBL) t);
The literal you put in the cardinality hint doesn't need to be particularly accurate, just close to general reality. If the number of rows is completely unknown the dynamic_sampling hint can help.
If you are using Oracle 11g, you may also benefit from cardinality feedback helping the optimizer learn to better estimate the number of elements in a collection.
Example if an ID is 1213 i want show **13.
If it's a number
select '**' || substr(to_char(id),3)
from my_table
Or, if it's already a character
select '**' || substr(id,3)
from my_table
This concatenates ** onto the beginning of the string, using the Oracle concatenation operator || and removes the first two characters of the id using substr.
Here's a SQL Fiddle to demonstrate.
If you don't want to sacrifice performance too much, to mask first two characters you can use-
SQL> select regexp_replace('1213','(.)2','**') from dual; --if VARCHAR
MASKED
------------
**13
SQL> select regexp_replace(1213,'(.)2','**') from dual; --if NUMBER
MASKED
------------
**13
REGEXP_REPLACE will work alike on NUMBER and VARCHAR so you save some conversion time there.
Consecutively, you can create a Function Based Index on the regexp function operation to optimize the query like (considering you would always want to mask only first two characters of ID) -
CREATE INDEX
mask_id
ON
table_name
(regexp_replace(id,'(.)2','**'));