Eliminate duplicates in ListAgg (Oracle)
https://dba.stackexchange.com/questions/696
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16-10-2019 - |
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Prior to Oracle 11.2 I was using a custom aggregate function to concatenate a column into a row. 11.2 Added the LISTAGG function, so I am trying to use that instead. My problem is that I need to eliminate duplicates in the results and don't seem to be able to do that.
Here is an example.
CREATE TABLE ListAggTest AS (
SELECT rownum Num1, DECODE(rownum,1,'2',to_char(rownum)) Num2 FROM dual
CONNECT BY rownum<=6
);
SELECT * FROM ListAggTest;
NUM1 NUM2
---------- ---------------------
1 2
2 2 << Duplicate 2
3 3
4 4
5 5
6 6
What I want to see is this:
NUM1 NUM2S
---------- --------------------
1 2-3-4-5-6
2 2-3-4-5-6
3 2-3-4-5-6
4 2-3-4-5-6
5 2-3-4-5-6
6 2-3-4-5-6
Here is a listagg version that is close, but doesn't eliminate duplicates.
SELECT Num1, listagg(Num2,'-') WITHIN GROUP (ORDER BY NULL) OVER () Num2s
FROM ListAggTest;
I have a solution, but it's worse than continuing to use the custom aggregate function.
المحلول
You can use regular expressions and regexp_replace to remove the duplicates after concatenation with listagg:
SELECT Num1,
RTRIM(
REGEXP_REPLACE(
(listagg(Num2,'-') WITHIN GROUP (ORDER BY Num2) OVER ()),
'([^-]*)(-\1)+($|-)',
'\1\3'),
'-') Num2s
FROM ListAggTest;
This could be tidier if Oracle's regex flavour supported lookahead or non-capturing groups, but it doesn't.
However this solution does avoid scanning the source more than once.
DBFiddle here
نصائح أخرى
As far as I can see, with the currently available language specification, this is
the shortest to achieve what you want if it must be done with listagg.
select distinct
a.Num1,
b.num2s
from listaggtest a cross join (
select listagg(num2d, '-') within group (order by num2d) num2s
from (
select distinct Num2 num2d from listaggtest
)
) b;
What was your solution that was worse than the custom aggregate solution?
Create a custom aggregate function to do this.
Oracle database provides a number of pre-defined aggregate functions such as MAX, MIN, SUM for performing operations on a set of records. These pre-defined aggregate functions can be used only with scalar data. However, you can create your own custom implementations of these functions, or define entirely new aggregate functions, to use with complex data—for example, with multimedia data stored using object types, opaque types, and LOBs.
User-defined aggregate functions are used in SQL DML statements just like the Oracle database built-in aggregates. Once such functions are registered with the server, the database simply invokes the aggregation routines that you supplied instead of the native ones.
User-defined aggregates can be used with scalar data as well. For example, it may be worthwhile to implement special aggregate functions for working with complex statistical data associated with financial or scientific applications.
User-defined aggregates are a feature of the Extensibility Framework. You implement them using ODCIAggregate interface routines.
Although this is an old post with an accepted answer, I think the LAG() analytic function works well in this case and is noteworthy:
- LAG() removes duplicate values in column num2 with minimal expense
- No need for non-trivial regular expression to filter results
- Just one full table scan (cost=4 on simple example table)
Here is the proposed code:
with nums as (
SELECT
num1,
num2,
decode( lag(num2) over (partition by null order by num2), --get last num2, if any
--if last num2 is same as this num2, then make it null
num2, null,
num2) newnum2
FROM ListAggTest
)
select
num1,
--listagg ignores NULL values, so duplicates are ignored
listagg( newnum2,'-') WITHIN GROUP (ORDER BY Num2) OVER () num2s
from nums;
The results below appear to be what the OP desires:
NUM1 NUM2S
1 2-3-4-5-6
2 2-3-4-5-6
3 2-3-4-5-6
4 2-3-4-5-6
5 2-3-4-5-6
6 2-3-4-5-6
Here was my solution to the problem which in my opinion isn't as nice as using our custom aggregate function which already exists.
SELECT Num1, listagg(Num2,'-') WITHIN GROUP (ORDER BY NULL) OVER () Num2s FROM (
SELECT Num1, DECODE(ROW_NUMBER() OVER (PARTITION BY Num2 ORDER BY NULL),
1,Num2,NULL) Num2 FROM ListAggTest
);
Use WMSYS.WM_Concat instead.
SELECT Num1, Replace(Wm_Concat(DISTINCT Num2) OVER (), ',', '-')
FROM ListAggTest;
Note: This function is undocumented and unsupported. See https://forums.oracle.com/forums/message.jspa?messageID=4372641#4372641.
You could also use a collect statement and then write a custom pl/sql function that converts the collection to a string.
CREATE TYPE varchar2_ntt AS TABLE OF VARCHAR2(4000);
CREATE TYPE varchar2_ntt AS TABLE OF VARCHAR2(4000);
select cast(collect(distinct num2 order by num2) as varchar2_ntt)
from listaggtest
You can use distinct and order by in a collect clause but if combined the distinct won't work as of 11.2.0.2 :(
Workaround could be a subselect:
select collect(num2 order by num2)
from
(
select distinct num2
from listaggtest
)
I created this solution before I encountered ListAgg, but there are still occasions, such as this duplicate value issue, then this tool is useful. The version below has 4 arguments to give you control over the results.
Explanation CLOBlist takes contructor CLOBlistParam as a parameter. CLOBlistParam has 4 arguments
string VARCHAR2(4000) - The variable to be aggregated
delimiter VARCHAR2(100) - The delimiting string
initiator VARCHAR2(100) - An initial string added before the first value only.
no_dup VARCHAR2(1) - A flag. Duplicates are suppressed if this is Y
Example usage
--vertical list of comma separated values, no duplicates.
SELECT CLOBlist(CLOBlistParam(column_name,chr(10)||',','','Y')) FROM user_tab_columns
--simple csv
SELECT CLOBlist(CLOBlistParam(table_name,',','','N')) FROM user_tables
Link to Gist is below.
https://gist.github.com/peter-genesys/d203bfb3d88d5a5664a86ea6ee34eeca]1
-- Program : CLOBlist
-- Name : CLOB list
-- Author : Peter Burgess
-- Purpose : CLOB list aggregation function for SQL
-- RETURNS CLOB - to allow for more than 4000 chars to be returned by SQL
-- NEW type CLOBlistParam - allows for definition of the delimiter, and initiator of sequence
------------------------------------------------------------------
--This is an aggregating function for use in SQL.
--It takes the argument and creates a comma delimited list of each instance.
WHENEVER SQLERROR CONTINUE
DROP TYPE CLOBlistImpl;
WHENEVER SQLERROR EXIT FAILURE ROLLBACK
create or replace type CLOBlistParam as object(
string VARCHAR2(4000)
,delimiter VARCHAR2(100)
,initiator VARCHAR2(100)
,no_dup VARCHAR2(1) )
/
show error
--Creating CLOBlist()
--Implement the type CLOBlistImpl to contain the ODCIAggregate routines.
create or replace type CLOBlistImpl as object
(
g_list CLOB, -- progressive concatenation
static function ODCIAggregateInitialize(sctx IN OUT CLOBlistImpl)
return number,
member function ODCIAggregateIterate(self IN OUT CLOBlistImpl
, value IN CLOBlistParam) return number,
member function ODCIAggregateTerminate(self IN CLOBlistImpl
, returnValue OUT CLOB
, flags IN number) return number,
member function ODCIAggregateMerge(self IN OUT CLOBlistImpl
, ctx2 IN CLOBlistImpl) return number
)
/
show error
--Implement the type body for CLOBlistImpl.
create or replace type body CLOBlistImpl is
static function ODCIAggregateInitialize(sctx IN OUT CLOBlistImpl)
return number is
begin
sctx := CLOBlistImpl(TO_CHAR(NULL));
return ODCIConst.Success;
end;
member function ODCIAggregateIterate(self IN OUT CLOBlistImpl
, value IN CLOBlistParam) return number is
begin
IF self.g_list IS NULL THEN
self.g_list := value.initiator||value.string;
ELSIF value.no_dup = 'Y' AND
value.delimiter||self.g_list||value.delimiter LIKE '%'||value.delimiter||value.string||value.delimiter||'%'
THEN
--Do not include duplicate value
NULL;
ELSE
self.g_list := self.g_list||value.delimiter||value.string;
END IF;
return ODCIConst.Success;
end;
member function ODCIAggregateTerminate(self IN CLOBlistImpl
, returnValue OUT CLOB
, flags IN number) return number is
begin
returnValue := self.g_list;
return ODCIConst.Success;
end;
member function ODCIAggregateMerge(self IN OUT CLOBlistImpl
, ctx2 IN CLOBlistImpl) return number is
begin
self.g_list := LTRIM( self.g_list||','||ctx2.g_list,',');
return ODCIConst.Success;
end;
end;
/
show error
--Using CLOBlist() to create a vertical list of comma separated values
-- SELECT CLOBlist(CLOBlistParam(product_code,chr(10)||',','','Y'))
-- FROM account
--DROP FUNCTION CLOBlist
--/
PROMPT Create the user-defined aggregate.
CREATE OR REPLACE FUNCTION CLOBlist (input CLOBlistParam) RETURN CLOB
PARALLEL_ENABLE AGGREGATE USING CLOBlistImpl;
/
show error
I know it's sometime after the original posting, but this was the first spot I found after Googling for an answer to the same problem and thought someone else who landed here might be happy to find a succinct answer that doesn't rely on overly complicated queries or regexes.
This will give you the desired result:
with nums as (
select distinct num2 distinct_nums
from listaggtest
order by num2
) select num1,
(select listagg(distinct_nums, '-') within group (order by 1) from nums) nums2list
from listaggtest;
My idea is to implement a stored function like this:
CREATE TYPE LISTAGG_DISTINCT_PARAMS AS OBJECT (ELEMENTO VARCHAR2(2000), SEPARATORE VARCHAR2(10));
CREATE TYPE T_LISTA_ELEMENTI AS TABLE OF VARCHAR2(2000);
CREATE TYPE T_LISTAGG_DISTINCT AS OBJECT (
LISTA_ELEMENTI T_LISTA_ELEMENTI,
SEPARATORE VARCHAR2(10),
STATIC FUNCTION ODCIAGGREGATEINITIALIZE(SCTX IN OUT T_LISTAGG_DISTINCT)
RETURN NUMBER,
MEMBER FUNCTION ODCIAGGREGATEITERATE (SELF IN OUT T_LISTAGG_DISTINCT,
VALUE IN LISTAGG_DISTINCT_PARAMS )
RETURN NUMBER,
MEMBER FUNCTION ODCIAGGREGATETERMINATE (SELF IN T_LISTAGG_DISTINCT,
RETURN_VALUE OUT VARCHAR2,
FLAGS IN NUMBER )
RETURN NUMBER,
MEMBER FUNCTION ODCIAGGREGATEMERGE (SELF IN OUT T_LISTAGG_DISTINCT,
CTX2 IN T_LISTAGG_DISTINCT )
RETURN NUMBER
);
CREATE OR REPLACE TYPE BODY T_LISTAGG_DISTINCT IS
STATIC FUNCTION ODCIAGGREGATEINITIALIZE(SCTX IN OUT T_LISTAGG_DISTINCT) RETURN NUMBER IS
BEGIN
SCTX := T_LISTAGG_DISTINCT(T_LISTA_ELEMENTI() , ',');
RETURN ODCICONST.SUCCESS;
END;
MEMBER FUNCTION ODCIAGGREGATEITERATE(SELF IN OUT T_LISTAGG_DISTINCT, VALUE IN LISTAGG_DISTINCT_PARAMS) RETURN NUMBER IS
BEGIN
IF VALUE.ELEMENTO IS NOT NULL THEN
SELF.LISTA_ELEMENTI.EXTEND;
SELF.LISTA_ELEMENTI(SELF.LISTA_ELEMENTI.LAST) := TO_CHAR(VALUE.ELEMENTO);
SELF.LISTA_ELEMENTI:= SELF.LISTA_ELEMENTI MULTISET UNION DISTINCT SELF.LISTA_ELEMENTI;
SELF.SEPARATORE := VALUE.SEPARATORE;
END IF;
RETURN ODCICONST.SUCCESS;
END;
MEMBER FUNCTION ODCIAGGREGATETERMINATE(SELF IN T_LISTAGG_DISTINCT, RETURN_VALUE OUT VARCHAR2, FLAGS IN NUMBER) RETURN NUMBER IS
STRINGA_OUTPUT CLOB:='';
LISTA_OUTPUT T_LISTA_ELEMENTI;
TERMINATORE VARCHAR2(3):='...';
LUNGHEZZA_MAX NUMBER:=4000;
BEGIN
IF SELF.LISTA_ELEMENTI.EXISTS(1) THEN -- se esiste almeno un elemento nella lista
-- inizializza una nuova lista di appoggio
LISTA_OUTPUT := T_LISTA_ELEMENTI();
-- riversamento dei soli elementi in DISTINCT
LISTA_OUTPUT := SELF.LISTA_ELEMENTI MULTISET UNION DISTINCT SELF.LISTA_ELEMENTI;
-- ordinamento degli elementi
SELECT CAST(MULTISET(SELECT * FROM TABLE(LISTA_OUTPUT) ORDER BY 1 ) AS T_LISTA_ELEMENTI ) INTO LISTA_OUTPUT FROM DUAL;
-- concatenazione in una stringa
FOR I IN LISTA_OUTPUT.FIRST .. LISTA_OUTPUT.LAST - 1
LOOP
STRINGA_OUTPUT := STRINGA_OUTPUT || LISTA_OUTPUT(I) || SELF.SEPARATORE;
END LOOP;
STRINGA_OUTPUT := STRINGA_OUTPUT || LISTA_OUTPUT(LISTA_OUTPUT.LAST);
-- se la stringa supera la dimensione massima impostata, tronca e termina con un terminatore
IF LENGTH(STRINGA_OUTPUT) > LUNGHEZZA_MAX THEN
RETURN_VALUE := SUBSTR(STRINGA_OUTPUT, 0, LUNGHEZZA_MAX - LENGTH(TERMINATORE)) || TERMINATORE;
ELSE
RETURN_VALUE:=STRINGA_OUTPUT;
END IF;
ELSE -- se non esiste nessun elemento, restituisci NULL
RETURN_VALUE := NULL;
END IF;
RETURN ODCICONST.SUCCESS;
END;
MEMBER FUNCTION ODCIAGGREGATEMERGE(SELF IN OUT T_LISTAGG_DISTINCT, CTX2 IN T_LISTAGG_DISTINCT) RETURN NUMBER IS
BEGIN
RETURN ODCICONST.SUCCESS;
END;
END; -- fine corpo
CREATE
FUNCTION LISTAGG_DISTINCT (INPUT LISTAGG_DISTINCT_PARAMS) RETURN VARCHAR2
PARALLEL_ENABLE AGGREGATE USING T_LISTAGG_DISTINCT;
// Example
SELECT LISTAGG_DISTINCT(LISTAGG_DISTINCT_PARAMS(OWNER, ', ')) AS LISTA_OWNER
FROM SYS.ALL_OBJECTS;
I'm sorry, but in some case (for a very big set), Oracle could return this error:
Object or Collection value was too large. The size of the value
might have exceeded 30k in a SORT context, or the size might be
too big for available memory.
but I think this is a good point of start ;)
Try this one:
select num1,listagg(Num2,'-') WITHIN GROUP (ORDER BY NULL) Num2s
from (
select distinct num1
,b.num2
from listaggtest a
,(
select num2
from listaggtest
) b
order by 1,2
)
group by num1
The issue with other possible solutions is that there is no correlation between the results for column 1 and column 2. To work around this the inner query creates this correlation and then removes the duplicates from that result set. When you do the listagg the result set is already clean. the problem had more to do with getting the data in a usable format.
SQL was designed as simple language, very close to english. So why don't you write it as in english?
- eliminate duplicates on num2 & use listagg as aggregate function - not analytic, to compute concat on string
- join in to original, as you want one result row for one input
select num1, num2s
from (select num2,
listagg(num2, '-') within group(order by num2) over() num2s
from listaggtest
group by num2
)
join listaggtest using (num2);
SELECT Num1, listagg(Num2,'-') WITHIN GROUP
(ORDER BY num1) OVER () Num2s FROM
(select distinct num1 from listAggTest) a,
(select distinct num2 from ListAggTest) b
where num1=num2(+);
The most effective solution is inner SELECT with GROUP BY, because DISTINCT and regular expressions are slow as hell.
SELECT num1, LISTAGG(num2, '-') WITHIN GROUP (ORDER BY num2) AS num2s
FROM (SELECT num1, num2
FROM ListAggTest
GROUP BY num1, num2)
GROUP BY num1;
This solution is pretty simple - first you get all unique combinations of num1 and num2 (inner SELECT) and then you get the string of all num2 grouped by num1.
