How to use Oracle aggregate function XMLAGG ?

You want to use Oracle aggregate function XMLAGG for string aggregation.?

Solution:

Example

SELECT class_id,
  rtrim(xmlagg(xmlelement(x,first_name
  || ' '
  || last_name , ', ')
ORDER BY first_name).extract('//text()').getstringval(), ',') AS "names"
FROM students
GROUP BY class_id;

Output

CL_MATH         ANDERSON DANIEL, MARTINEZ CHRISTOPHER, TAYLOR PAUL, THOMAS MARK, WILSON THOMAS,
CL_PHY          RODRIGUEZ JOSEPH,
INS_CHAIRMAN    SMITH JAMES,
INS_STAFF       BROWN MICHAEL, DAVIS RICHARD, GARCIA CHARLES, JONES WILLIAM, MILLER DAVID,
INS_VP          JOHNSON JOHN, WILLIAMS ROBERT,

In the above statement xmlelement will create an XML element called x (name it what ever you want) containing a concatenation of the first_name, last_name and a comma.

The xmlagg creates an XML snippet that is an aggregation of the x XML elements. “.extract(‘//text()’)” get rids of xml keeping the string alone. Finally we will remove trailing comma in the aggregated text using rtrim.

If you want to use CLOB rather than a string then see below code. The function xmlparse takes xml as text and transforms it to XMLType datatype.

Example

SELECT class_id,
  xmlagg(xmlparse(content first_name
  || ' '
  || last_name wellformed)
ORDER BY first_name).getclobval()
FROM students
GROUP BY class_id;

Output

CL_MATH         ANDERSON DANIELMARTINEZ CHRISTOPHERTAYLOR PAULTHOMAS MARKWILSON THOMAS
CL_PHY          RODRIGUEZ JOSEPH
INS_CHAIRMAN    SMITH JAMES
INS_STAFF       BROWN MICHAELDAVIS RICHARDGARCIA CHARLESJONES WILLIAMMILLER DAVID
INS_VP          JOHNSON JOHNWILLIAMS ROBERT

The result is a CLOB which is displayed in the output. If the database version is 18c or later then json_arrayagg can be used as an alternative to xmlagg.

Example

SELECT class_id,
      replace(JSON_ARRAYAGG(first_name || ' ' || last_name ORDER BY class_id RETURNING CLOB),'"','') AS retunring_val
FROM students
GROUP BY class_id;

Output

CL_MATH         [WILSON THOMAS,THOMAS MARK,TAYLOR PAUL,ANDERSON DANIEL,MARTINEZ CHRISTOPHER]
CL_PHY          [RODRIGUEZ JOSEPH]
INS_CHAIRMAN    [SMITH JAMES]
INS_STAFF       [BROWN MICHAEL,GARCIA CHARLES,DAVIS RICHARD,MILLER DAVID,JONES WILLIAM]
INS_VP          [JOHNSON JOHN,WILLIAMS ROBERT]

Data Preparation: Data used for the problem is shown below.

Example

DROP TABLE students;
COMMIT;

CREATE TABLE students
    ( student_id     NUMBER(6)
    , first_name     VARCHAR2(20)
    , last_name      VARCHAR2(25) 
    , email          VARCHAR2(40) 
    , phone_number   VARCHAR2(20)
    , join_date      DATE 
    , class_id       VARCHAR2(20)  
    , fees           NUMBER(8,2)
    , professor_id   NUMBER(6)
    , department_id  NUMBER(4) 
    ) ;

Example

CREATE UNIQUE INDEX stu_id_pk ON students (student_id) ;
INSERT INTO students VALUES (100,'SMITH','JAMES','SMITH.JAMES@notreal.com','111.111.1245',TO_DATE('17-06-2003','DD-MM-YYYY'),'INS_CHAIRMAN',24000,NULL,NULL);
INSERT INTO students VALUES (101,'JOHNSON','JOHN','JOHNSON.JOHN@notreal.com','111.111.1246',TO_DATE('21-09-2005','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (102,'WILLIAMS','ROBERT','WILLIAMS.ROBERT@notreal.com','111.111.1247',TO_DATE('13-01-2001','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (103,'BROWN','MICHAEL','BROWN.MICHAEL@notreal.com','111.111.1248',TO_DATE('03-01-2006','DD-MM-YYYY'),'INS_STAFF',9000,102,60);
INSERT INTO students VALUES (104,'JONES','WILLIAM','JONES.WILLIAM@notreal.com','111.111.1249',TO_DATE('21-05-2007','DD-MM-YYYY'),'INS_STAFF',6000,103,60);
INSERT INTO students VALUES (105,'MILLER','DAVID','MILLER.DAVID@notreal.com','111.111.1250',TO_DATE('25-06-2005','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (106,'DAVIS','RICHARD','DAVIS.RICHARD@notreal.com','111.111.1251',TO_DATE('05-02-2006','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (107,'GARCIA','CHARLES','GARCIA.CHARLES@notreal.com','111.111.1252',TO_DATE('07-02-2007','DD-MM-YYYY'),'INS_STAFF',4200,103,60);
INSERT INTO students VALUES (108,'RODRIGUEZ','JOSEPH','RODRIGUEZ.JOSEPH@notreal.com','111.111.1253',TO_DATE('17-08-2002','DD-MM-YYYY'),'CL_PHY',12008,101,100);
INSERT INTO students VALUES (109,'WILSON','THOMAS','WILSON.THOMAS@notreal.com','111.111.1254',TO_DATE('16-08-2002','DD-MM-YYYY'),'CL_MATH',9000,108,100);
INSERT INTO students VALUES (110,'MARTINEZ','CHRISTOPHER','MARTINEZ.CHRISTOPHER@notreal.com','111.111.1255',TO_DATE('28-09-2005','DD-MM-YYYY'),'CL_MATH',8200,108,100);
INSERT INTO students VALUES (111,'ANDERSON','DANIEL','ANDERSON.DANIEL@notreal.com','111.111.1256',TO_DATE('30-09-2005','DD-MM-YYYY'),'CL_MATH',7700,108,100);
INSERT INTO students VALUES (112,'TAYLOR','PAUL','TAYLOR.PAUL@notreal.com','111.111.1257',TO_DATE('07-03-2006','DD-MM-YYYY'),'CL_MATH',7800,108,100);
INSERT INTO students VALUES (113,'THOMAS','MARK','THOMAS.MARK@notreal.com','111.111.1258',TO_DATE('07-12-2007','DD-MM-YYYY'),'CL_MATH',6900,108,100);

COMMIT;