Oracle 中的 LISTAGG 返回不同的值

Question

I am trying to use the LISTAGG function in Oracle. I would like to get only the distinct values for that column. Is there a way in which I can get only the distinct values without creating a function or a procedure?

  col1  col2 Created_by
   1     2     Smith 
   1     2     John 
   1     3     Ajay 
   1     4     Ram 
   1     5     Jack 

I need to select col1 and the LISTAGG of col2 (column 3 is not considered). When I do that, I get something like this as the result of LISTAGG : [2,2,3,4,5]

I need to remove the duplicate '2' here; I need only the distinct values of col2 against col1.

Answer 1

19c and later:

select listagg(distinct the_column, ',') within group (order by the_column)
from the_table

18c and earlier:

select listagg(the_column, ',') within group (order by the_column)
from (
   select distinct the_column 
   from the_table
) t

If you need more columns, something like this might be what you are looking for:

select col1, listagg(col2, ',') within group (order by col2)
from (
  select col1, 
         col2,
         row_number() over (partition by col1, col2 order by col1) as rn
  from foo
  order by col1,col2
)
where rn = 1
group by col1;

Answer 2

From oracle 19C it is built in see here

From 18C and earlier try within group see here

Otherwise use regular expressions

Here's how to solve your issue.

select  
      regexp_replace(
    '2,2,2.1,3,3,3,3,4,4' 
     ,'([^,]+)(,\1)*(,|$)', '\1\3')

from dual

returns

2,2.1,3,4

ANSWER below:

select col1, 

regexp_replace(
    listagg(
     col2 , ',') within group (order by col2)  -- sorted
    ,'([^,]+)(,\1)*(,|$)', '\1\3') )
   from tableX
where rn = 1
group by col1; 

Note: The above will work in most cases - list should be sorted , you may have to trim all trailing and leading space depending on your data.

If you have a alot of items in a group > 20 or big string sizes you might run into oracle string size limit 'result of string concatenation is too long'.

From oracle 12cR2 you can suppress this error see here . Alternatively put a max number on the members in each group. This will only work if its ok to list only the first members. If you have very long variable strings this may not work. you will have to experiment.

select col1,

case 
    when count(col2) < 100 then 
       regexp_replace(
        listagg(col2, ',') within group (order by col2)
        ,'([^,]+)(,\1)*(,|$)', '\1\3')
 
    else
    'Too many entries to list...'
end
    
from sometable
where rn = 1
group by col1;

Another solution (not so simple) to hopefully avoid oracle string size limit - string size is limited to 4000. Thanks to this post here by user3465996

select col1  ,
    dbms_xmlgen.convert(  -- HTML decode
    dbms_lob.substr( -- limit size to 4000 chars
    ltrim( -- remove leading commas
    REGEXP_REPLACE(REPLACE(
         REPLACE(
           XMLAGG(
             XMLELEMENT("A",col2 )
               ORDER BY col2).getClobVal(),
             '<A>',','),
             '</A>',''),'([^,]+)(,\1)*(,|$)', '\1\3'),
                  ','), -- remove leading XML commas ltrim
                      4000,1) -- limit to 4000 string size
                      , 1)  -- HTML.decode
                       as col2
 from sometable
where rn = 1
group by col1;

V1 - some test cases - FYI

regexp_replace('2,2,2.1,3,3,4,4','([^,]+)(,\1)+', '\1')
-> 2.1,3,4 Fail
regexp_replace('2 ,2 ,2.1,3 ,3 ,4 ,4 ','([^,]+)(,\1)+', '\1')
-> 2 ,2.1,3,4 Success  - fixed length items

V2 -items contained within items eg. 2,21

regexp_replace('2.1,1','([^,]+)(,\1)+', '\1')
-> 2.1 Fail
regexp_replace('2 ,2 ,2.1,1 ,3 ,4 ,4 ','(^|,)(.+)(,\2)+', '\1\2')
-> 2 ,2.1,1 ,3 ,4  -- success - NEW regex
 regexp_replace('a,b,b,b,b,c','(^|,)(.+)(,\2)+', '\1\2')
-> a,b,b,c fail!

v3 - regex thank Igor! works all cases.

select  
regexp_replace('2,2,2.1,3,3,4,4','([^,]+)(,\1)*(,|$)', '\1\3') ,
---> 2,2.1,3,4 works
regexp_replace('2.1,1','([^,]+)(,\1)*(,|$)', '\1\3'),
--> 2.1,1 works
regexp_replace('a,b,b,b,b,c','([^,]+)(,\1)*(,|$)', '\1\3')
---> a,b,c works

from dual

Answer 3

you can use undocumented wm_concat function.

select col1, wm_concat(distinct col2) col2_list 
from tab1
group by col1;

this function returns clob column, if you want you can use dbms_lob.substr to convert clob to varchar2.

Answer 4

If you want distinct values across MULTIPLE columns, want control over sort order, don't want to use an undocumented function that may disappear, and do not want more than one full table scan, you may find this construct useful:

with test_data as 
(
      select 'A' as col1, 'T_a1' as col2, '123' as col3 from dual
union select 'A', 'T_a1', '456' from dual
union select 'A', 'T_a1', '789' from dual
union select 'A', 'T_a2', '123' from dual
union select 'A', 'T_a2', '456' from dual
union select 'A', 'T_a2', '111' from dual
union select 'A', 'T_a3', '999' from dual
union select 'B', 'T_a1', '123' from dual
union select 'B', 'T_b1', '740' from dual
union select 'B', 'T_b1', '846' from dual
)
select col1
     , (select listagg(column_value, ',') within group (order by column_value desc) from table(collect_col2)) as col2s
     , (select listagg(column_value, ',') within group (order by column_value desc) from table(collect_col3)) as col3s
from 
(
select col1
     , collect(distinct col2) as collect_col2
     , collect(distinct col3) as collect_col3
from test_data
group by col1
);

Answer 5

I overcame this issue by grouping on the values first, then do another aggregation with the listagg. Something like this:

select a,b,listagg(c,',') within group(order by c) c, avg(d)
from (select a,b,c,avg(d)
      from   table
      group by (a,b,c))
group by (a,b)

only one full table access, relatively easy to expand to more complex queries

Answer 6

If the intent is to apply this transformation to multiple columns, I have extended a_horse_with_no_name's solution:

SELECT * FROM
(SELECT LISTAGG(GRADE_LEVEL, ',') within group(order by GRADE_LEVEL) "Grade Levels" FROM (select distinct GRADE_LEVEL FROM Students) t)                     t1,
(SELECT LISTAGG(ENROLL_STATUS, ',') within group(order by ENROLL_STATUS) "Enrollment Status" FROM (select distinct ENROLL_STATUS FROM Students) t)          t2,
(SELECT LISTAGG(GENDER, ',') within group(order by GENDER) "Legal Gender Code" FROM (select distinct GENDER FROM Students) t)                               t3,
(SELECT LISTAGG(CITY, ',') within group(order by CITY) "City" FROM (select distinct CITY FROM Students) t)                                                  t4,
(SELECT LISTAGG(ENTRYCODE, ',') within group(order by ENTRYCODE) "Entry Code" FROM (select distinct ENTRYCODE FROM Students) t)                             t5,
(SELECT LISTAGG(EXITCODE, ',') within group(order by EXITCODE) "Exit Code" FROM (select distinct EXITCODE FROM Students) t)                                 t6,
(SELECT LISTAGG(LUNCHSTATUS, ',') within group(order by LUNCHSTATUS) "Lunch Status" FROM (select distinct LUNCHSTATUS FROM Students) t)                     t7,
(SELECT LISTAGG(ETHNICITY, ',') within group(order by ETHNICITY) "Race Code" FROM (select distinct ETHNICITY FROM Students) t)                              t8,
(SELECT LISTAGG(CLASSOF, ',') within group(order by CLASSOF) "Expected Graduation Year" FROM (select distinct CLASSOF FROM Students) t)                     t9,
(SELECT LISTAGG(TRACK, ',') within group(order by TRACK) "Track Code" FROM (select distinct TRACK FROM Students) t)                                         t10,
(SELECT LISTAGG(GRADREQSETID, ',') within group(order by GRADREQSETID) "Graduation ID" FROM (select distinct GRADREQSETID FROM Students) t)                 t11,
(SELECT LISTAGG(ENROLLMENT_SCHOOLID, ',') within group(order by ENROLLMENT_SCHOOLID) "School Key" FROM (select distinct ENROLLMENT_SCHOOLID FROM Students) t)       t12,
(SELECT LISTAGG(FEDETHNICITY, ',') within group(order by FEDETHNICITY) "Federal Race Code" FROM (select distinct FEDETHNICITY FROM Students) t)                         t13,
(SELECT LISTAGG(SUMMERSCHOOLID, ',') within group(order by SUMMERSCHOOLID) "Summer School Key" FROM (select distinct SUMMERSCHOOLID FROM Students) t)                               t14,
(SELECT LISTAGG(FEDRACEDECLINE, ',') within group(order by FEDRACEDECLINE) "Student Decl to Prov Race Code" FROM (select distinct FEDRACEDECLINE FROM Students) t)          t15

This is Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production.
I was unable to use STRAGG because there is no way to DISTINCT and ORDER.

Performance scales linearly, which is good, since I am adding all columns of interest. The above took 3 seconds for 77K rows. For just one rollup, .172 seconds. I do with there was a way to distinctify multiple columns in a table in one pass.

Answer 7

Upcoming Oracle 19c will support DISTINCT with LISTAGG .

LISTAGG with DISTINCT option :

This feature is coming with 19c:

 SQL> select deptno, listagg (distinct sal,', ') within group (order by sal) 2 from scott.emp 3 group by deptno;

---

EDIT:

Oracle 19C LISTAGG DISTINCT

The LISTAGG aggregate function now supports duplicate elimination by using the new DISTINCT keyword. The LISTAGG aggregate function orders the rows for each group in a query according to the ORDER BY expression and then concatenates the values into a single string. With the new DISTINCT keyword, duplicate values can be removed from the specified expression before concatenation into a single string. This removes the need to create complex query processing to find the distinct values prior to using the aggregate LISTAGG function. With the DISTINCT option, the processing to remove duplicate values can be done directly within the LISTAGG function. The result is simpler, faster, more efficient SQL.

Answer 8

To get around the string length issue you can use XMLAGG which is similar to listagg but it returns a clob.

You can can then parse using regexp_replace and get the unique values and then turn it back into a string using dbms_lob.substr() . If you have a huge amount of distinct values you will still run out of space this way but for a lot of cases the code below should work.

You can also change the delimiters you use. In my case I wanted '-' instead of ',' but you should be able to replace the dashes in my code and use commas if you want that.

select col1,
    dbms_lob.substr(ltrim(REGEXP_REPLACE(REPLACE(
         REPLACE(
           XMLAGG(
             XMLELEMENT("A",col2)
               ORDER BY col2).getClobVal(),
             '<A>','-'),
             '</A>',''),'([^-]*)(-\1)+($|-)', 
           '\1\3'),'-'), 4000,1) as platform_mix
from table

Answer 9

What about creating a dedicated function that will make the "distinct" part :

create or replace function listagg_distinct (t in str_t, sep IN VARCHAR2 DEFAULT ',') 
  return VARCHAR2
as 
  l_rc VARCHAR2(4096) := '';
begin
  SELECT listagg(val, sep) WITHIN GROUP (ORDER BY 1)
    INTO l_rc
    FROM (SELECT DISTINCT column_value val FROM table(t));
  RETURN l_rc;
end;
/

And then use it to do the aggregation :

SELECT col1, listagg_distinct(cast(collect(col_2) as str_t ), ', ')
  FROM your_table
  GROUP BY col_1;

Answer 10

Further refining @YoYo's correction to @a_horse_with_no_name's row_number() based approach using DECODE vs CASE ( i saw here ). I see that @Martin Vrbovsky also has this case approach answer.

select
  col1, 
  listagg(col2, ',') within group (order by col2) AS col2_list,
  listagg(col3, ',') within group (order by col3) AS col3_list,
  SUM(col4) AS col4
from (
  select
    col1, 
    decode(row_number() over (partition by col1, col2 order by null),1,col2) as col2,
    decode(row_number() over (partition by col1, col3 order by null),1,col3) as col3
  from foo
)
group by col1;

Answer 11

listagg() ignores NULL values, so in a first step you could use the lag() function to analyse whether the previous record had the same value, if yes then NULL, else 'new value'.

WITH tab AS 
(           
          SELECT 1 as col1, 2 as col2, 'Smith' as created_by FROM dual
UNION ALL SELECT 1 as col1, 2 as col2, 'John'  as created_by FROM dual
UNION ALL SELECT 1 as col1, 3 as col2, 'Ajay'  as created_by FROM dual
UNION ALL SELECT 1 as col1, 4 as col2, 'Ram'   as created_by FROM dual
UNION ALL SELECT 1 as col1, 5 as col2, 'Jack'  as created_by FROM dual
)
SELECT col1
     , CASE 
       WHEN lag(col2) OVER (ORDER BY col2) = col2 THEN 
         NULL 
       ELSE 
         col2 
       END as col2_with_nulls
     , created_by
  FROM tab;

Results

      COL1 COL2_WITH_NULLS CREAT
---------- --------------- -----
         1               2 Smith
         1                 John
         1               3 Ajay
         1               4 Ram
         1               5 Jack

Note that the second 2 is replaced by NULL. Now you can wrap a SELECT with the listagg() around it.

WITH tab AS 
(           
          SELECT 1 as col1, 2 as col2, 'Smith' as created_by FROM dual
UNION ALL SELECT 1 as col1, 2 as col2, 'John'  as created_by FROM dual
UNION ALL SELECT 1 as col1, 3 as col2, 'Ajay'  as created_by FROM dual
UNION ALL SELECT 1 as col1, 4 as col2, 'Ram'   as created_by FROM dual
UNION ALL SELECT 1 as col1, 5 as col2, 'Jack'  as created_by FROM dual
)
SELECT listagg(col2_with_nulls, ',') WITHIN GROUP (ORDER BY col2_with_nulls) col2_list
  FROM ( SELECT col1
              , CASE WHEN lag(col2) OVER (ORDER BY col2) = col2 THEN NULL ELSE col2 END as col2_with_nulls
              , created_by
           FROM tab );

Result

COL2_LIST
---------
2,3,4,5

You can do this over multiple columns too.

WITH tab AS 
(           
          SELECT 1 as col1, 2 as col2, 'Smith' as created_by FROM dual
UNION ALL SELECT 1 as col1, 2 as col2, 'John'  as created_by FROM dual
UNION ALL SELECT 1 as col1, 3 as col2, 'Ajay'  as created_by FROM dual
UNION ALL SELECT 1 as col1, 4 as col2, 'Ram'   as created_by FROM dual
UNION ALL SELECT 1 as col1, 5 as col2, 'Jack'  as created_by FROM dual
)
SELECT listagg(col1_with_nulls, ',') WITHIN GROUP (ORDER BY col1_with_nulls) col1_list
     , listagg(col2_with_nulls, ',') WITHIN GROUP (ORDER BY col2_with_nulls) col2_list
     , listagg(created_by, ',')      WITHIN GROUP (ORDER BY created_by) created_by_list
  FROM ( SELECT CASE WHEN lag(col1) OVER (ORDER BY col1) = col1 THEN NULL ELSE col1 END as col1_with_nulls
              , CASE WHEN lag(col2) OVER (ORDER BY col2) = col2 THEN NULL ELSE col2 END as col2_with_nulls
              , created_by
           FROM tab );

Result

COL1_LIST COL2_LIST CREATED_BY_LIST
--------- --------- -------------------------
1         2,3,4,5   Ajay,Jack,John,Ram,Smith

Answer 12

I implemented this stored function :

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 ;)

Answer 13

Has anyone thought of using a PARTITION BY clause? It worked for me in this query to get a list of application services and the access.

SELECT DISTINCT T.APP_SVC_ID, 
       LISTAGG(RTRIM(T.ACCESS_MODE), ',') WITHIN GROUP(ORDER BY T.ACCESS_MODE) OVER(PARTITION BY T.APP_SVC_ID) AS ACCESS_MODE 
  FROM APP_SVC_ACCESS_CNTL T 
 GROUP BY T.ACCESS_MODE, T.APP_SVC_ID

I had to cut out my where clause for NDA, but you get the idea.

Answer 14

I think this could help - CASE the columns value to NULL if it's duplicate - then it's not appended to LISTAGG string:

with test_data as 
(
      select 1 as col1, 2 as col2, 'Smith' as created_by from dual
union select 1, 2, 'John' from dual
union select 1, 3, 'Ajay' from dual
union select 1, 4, 'Ram' from dual
union select 1, 5, 'Jack' from dual
union select 2, 5, 'Smith' from dual
union select 2, 6, 'John' from dual
union select 2, 6, 'Ajay' from dual
union select 2, 6, 'Ram' from dual
union select 2, 7, 'Jack' from dual
)
SELECT col1  ,
      listagg(col2 , ',') within group (order by col2 ASC) AS orig_value,
      listagg(CASE WHEN rwn=1 THEN col2 END , ',') within group (order by col2 ASC) AS distinct_value
from 
    (
    select row_number() over (partition by col1,col2 order by 1) as rwn, 
           a.*
    from test_data a
    ) a
GROUP BY col1   

Results in:

COL1  ORIG         DISTINCT
1   2,2,3,4,5   2,3,4,5
2   5,6,6,6,7   5,6,7

Answer 15

You can do it via RegEx replacement. Here is an example:

-- Citations Per Year - Cited Publications main query. Includes list of unique associated core project numbers, ordered by core project number.
SELECT ptc.pmid AS pmid, ptc.pmc_id, ptc.pub_title AS pubtitle, ptc.author_list AS authorlist,
  ptc.pub_date AS pubdate,
  REGEXP_REPLACE( LISTAGG ( ppcc.admin_phs_org_code || 
    TO_CHAR(ppcc.serial_num,'FM000000'), ',') WITHIN GROUP (ORDER BY ppcc.admin_phs_org_code || 
    TO_CHAR(ppcc.serial_num,'FM000000')),
    '(^|,)(.+)(,\2)+', '\1\2')
  AS projectNum
FROM publication_total_citations ptc
  JOIN proj_paper_citation_counts ppcc
    ON ptc.pmid = ppcc.pmid
   AND ppcc.citation_year = 2013
  JOIN user_appls ua
    ON ppcc.admin_phs_org_code = ua.admin_phs_org_code
   AND ppcc.serial_num = ua.serial_num
   AND ua.login_id = 'EVANSF'
GROUP BY ptc.pmid, ptc.pmc_id, ptc.pub_title, ptc.author_list, ptc.pub_date
ORDER BY pmid;

Also posted here: Oracle - unique Listagg values

Answer 16

I wrote a function to handle this using regular expressions. The in parameters are: 1) the listagg call itself 2) A repeat of the delimiter

create or replace function distinct_listagg
  (listagg_in varchar2,
   delimiter_in varchar2)

   return varchar2
   as
   hold_result varchar2(4000);
   begin

   select rtrim( regexp_replace( (listagg_in)
      , '([^'||delimiter_in||']*)('||
      delimiter_in||'\1)+($|'||delimiter_in||')', '\1\3'), ',')
      into hold_result
      from dual;

return hold_result;

end;

Now you don't have to repeat the regular expression every time you do this, simply say:

select distinct_listagg(
                       listagg(myfield,', ') within group (order by 1),
                       ', '
                       )
     from mytable;

Answer 17

If you do not need a particular order of concatenated values, and the separator can be a comma, you can do:

select col1, stragg(distinct col2)
  from table
 group by col1

Answer 18

I neded a DISTINCT version of this and got this one working out.

RTRIM(REGEXP_REPLACE(
                       (value, ', ') WITHIN GROUP( ORDER BY value)), 
                            '([^ ]+)(, \1)+','\1'),', ') 

Answer 19

One annoying aspect with LISTAGG is that if the total length of concatenated string exceeds 4000 characters( limit for VARCHAR2 in SQL ), the below error is thrown, which is difficult to manage in Oracle versions upto 12.1

ORA-01489: result of string concatenation is too long

A new feature added in 12cR2 is the ON OVERFLOW clause of LISTAGG . The query including this clause would look like:

SELECT pid, LISTAGG(Desc, ' ' on overflow truncate) WITHIN GROUP (ORDER BY seq) AS desc
FROM B GROUP BY pid;

The above will restrict the output to 4000 characters but will not throw the ORA-01489 error.

These are some of the additional options of ON OVERFLOW clause:

• ON OVERFLOW TRUNCATE 'Contd..' : This will display 'Contd..' at the end of string (Default is ... )
• ON OVERFLOW TRUNCATE '' : This will display the 4000 characters without any terminating string.
• ON OVERFLOW TRUNCATE WITH COUNT : This will display the total number of characters at the end after the terminating characters. Eg:- ' ...(5512) '
• ON OVERFLOW ERROR : If you expect the LISTAGG to fail with the ORA-01489 error ( Which is default anyway ).

Answer 20

Using SELECT DISTINCT ... as part of a Subquery before calling LISTAGG is probably the best way for simple queries, as noted by @a_horse_with_no_name

However, in more complex queries, it might not be possible, or easy, to accomplish this. I had this come up in a scenario that was using top-n approach using an analytic function.

So I found the COLLECT aggregate function. It is documented to have the UNIQUE or DISTINCT modifier available. Only in 10g , it quietly fails (it ignores the modifier without error). However, to overcome this, from another answer , I came to this solution:

SELECT
  ...
  (
    SELECT LISTAGG(v.column_value,',') WITHIN GROUP (ORDER BY v.column_value)
    FROM TABLE(columns_tab) v
  ) AS columns,
  ...
FROM (
  SELECT
    ...
    SET(CAST(COLLECT(UNIQUE some_column ORDER BY some_column) AS tab_typ)) AS columns_tab,
    ...
)

Basically, by using SET , I remove the duplicates in my collection.

You would still need to define the tab_typ as a basic collection type, and in the case of a VARCHAR , this would be for example:

CREATE OR REPLACE type tab_typ as table of varchar2(100)
/

Also as a correction to the answer from @a_horse_with_no_name on the multi column situation, where you might want to aggregate still on a third (or more) columns:

select
  col1, 
  listagg(CASE rn2 WHEN 1 THEN col2 END, ',') within group (order by col2) AS col2_list,
  listagg(CASE rn3 WHEN 1 THEN col3 END, ',') within group (order by col3) AS col3_list,
  SUM(col4) AS col4
from (
  select
    col1, 
    col2,
    row_number() over (partition by col1, col2 order by null) as rn2,
    row_number() over (partition by col1, col3 order by null) as rn3
  from foo
)
group by col1;

If you would leave the rn = 1 as a where condition to the query, you would aggregate other columns incorrectly.

Answer 21

select col1, listaggr(col2,',') within group(Order by col2) from table group by col1 meaning aggregate the strings (col2) into list keeping the order n then afterwards deal with the duplicates as group by col1 meaning merge col1 duplicates in 1 group. perhaps this looks clean and simple as it should be and if in case you want col3 as well just you need to add one more listagg() that is select col1, listaggr(col2,',') within group(Order by col2),listaggr(col3,',') within group(order by col3) from table group by col1

Answer 22

Use listagg_clob function created like this:

create or replace package list_const_p
is
list_sep varchar2(10) := ',';
end list_const_p;
/
sho err

create type listagg_clob_t as object(
v_liststring varchar2(32767),
v_clob clob,
v_templob number,

static function ODCIAggregateInitialize(
sctx IN OUT listagg_clob_t
) return number,
member function ODCIAggregateIterate(
self IN OUT listagg_clob_t, value IN varchar2
) return number,
member function ODCIAggregateTerminate(
self IN OUT listagg_clob_t, returnValue OUT clob, flags IN number
) return number,
member function ODCIAggregateMerge(
self IN OUT listagg_clob_t, ctx2 IN OUT listagg_clob_t
) return number
);
/
sho err

create or replace type body listagg_clob_t is

static function ODCIAggregateInitialize(sctx IN OUT listagg_clob_t)
return number is
begin
sctx := listagg_clob_t('', '', 0);
return ODCIConst.Success;
end;

member function ODCIAggregateIterate(
self IN OUT listagg_clob_t,
value IN varchar2
) return number is
begin
if nvl(lengthb(v_liststring),0) + nvl(lengthb(value),0) <= 4000 then
self.v_liststring:=self.v_liststring || value || list_const_p.list_sep;
else
if self.v_templob = 0 then
dbms_lob.createtemporary(self.v_clob, true, dbms_lob.call);
self.v_templob := 1;
end if;
dbms_lob.writeappend(self.v_clob, length(self.v_liststring), v_liststring);
self.v_liststring := value || list_const_p.list_sep;
end if;
return ODCIConst.Success;
end;

member function ODCIAggregateTerminate(
self IN OUT listagg_clob_t,
returnValue OUT clob,
flags IN number
) return number is
begin
if self.v_templob != 0 then
dbms_lob.writeappend(self.v_clob, length(self.v_liststring), self.v_liststring);
dbms_lob.trim(self.v_clob, dbms_lob.getlength(self.v_clob) - 1);
else
self.v_clob := substr(self.v_liststring, 1, length(self.v_liststring) - 1);
end if;
returnValue := self.v_clob;
return ODCIConst.Success;
end;

member function ODCIAggregateMerge(self IN OUT listagg_clob_t, ctx2 IN OUT listagg_clob_t) return number is
begin
if ctx2.v_templob != 0 then
if self.v_templob != 0 then
dbms_lob.append(self.v_clob, ctx2.v_clob);
dbms_lob.freetemporary(ctx2.v_clob);
ctx2.v_templob := 0;
else
self.v_clob := ctx2.v_clob;
self.v_templob := 1;
ctx2.v_clob := '';
ctx2.v_templob := 0;
end if;
end if;
if nvl(lengthb(self.v_liststring),0) + nvl(lengthb(ctx2.v_liststring),0) <= 4000 then
self.v_liststring := self.v_liststring || ctx2.v_liststring;
ctx2.v_liststring := '';
else
if self.v_templob = 0 then
dbms_lob.createtemporary(self.v_clob, true, dbms_lob.call);
self.v_templob := 1;
end if;
dbms_lob.writeappend(self.v_clob, length(self.v_liststring), self.v_liststring);
dbms_lob.writeappend(self.v_clob, length(ctx2.v_liststring), ctx2.v_liststring);
self.v_liststring := '';
ctx2.v_liststring := '';
end if;
return ODCIConst.Success;
end;
end;
/
sho err

CREATE or replace FUNCTION listagg_clob (input varchar2) RETURN clob
PARALLEL_ENABLE AGGREGATE USING listagg_clob_t;
/
sho err 

Answer 23

The simplest way to handle multiple listagg's is to use 1 WITH (subquery factor) per column containing a listagg of that column from a select distinct:

    WITH tab AS 
    (           
        SELECT 1 as col1, 2 as col2, 3 as col3, 'Smith' as created_by FROM dual
        UNION ALL SELECT 1 as col1, 2 as col2, 3 as col3,'John'  as created_by FROM dual
        UNION ALL SELECT 1 as col1, 3 as col2, 4 as col3,'Ajay'  as created_by FROM dual
        UNION ALL SELECT 1 as col1, 4 as col2, 4 as col3,'Ram'   as created_by FROM dual
        UNION ALL SELECT 1 as col1, 5 as col2, 6 as col3,'Jack'  as created_by FROM dual
    )
    , getCol2 AS
    (
        SELECT  DISTINCT col1, listagg(col2,',') within group (order by col2)  over (partition by col1) AS col2List
        FROM ( SELECT DISTINCT col1,col2 FROM tab)
    )
    , getCol3 AS
    (
        SELECT  DISTINCT col1, listagg(col3,',') within group (order by col3)  over (partition by col1) AS col3List
        FROM ( SELECT DISTINCT col1,col3 FROM tab)
    )
    select col1,col2List,col3List
    FROM getCol2
    JOIN getCol3
    using (col1)

Which gives:

col1  col2List  col3List
1     2,3,4,5   3,4,6

Answer 24

Very simple - use in your query a sub-query with a select distinct:

SELECT question_id,
       LISTAGG(element_id, ',') WITHIN GROUP (ORDER BY element_id)
FROM
       (SELECT distinct question_id, element_id
       FROM YOUR_TABLE)
GROUP BY question_id;