Collecting data from multiple rows into one column

Question

I'd like to run a query and put a collection of items into one output column instead of multiple rows. See the example below:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - Prod
PL/SQL Release 10.2.0.5.0 - Production
"CORE     10.2.0.5.0     Production"
TNS for 32-bit Windows: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - Production
     CREATE TABLE "SKIP"."INGREDIENTS"
   (     "INGRED_ID" NUMBER,
     "INGRED_NAME" VARCHAR2(20 BYTE),
     "STORES" VARCHAR2(20 BYTE)
   ) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
  STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
  TABLESPACE "USERS" ;
REM INSERTING into SKIP.INGREDIENTS
Insert into SKIP.INGREDIENTS (INGRED_ID,INGRED_NAME,STORES) values (1,'SEA SALT','Food lion');
Insert into SKIP.INGREDIENTS (INGRED_ID,INGRED_NAME,STORES) values (2,'TABLE SALT','Food lion');
Insert into SKIP.INGREDIENTS (INGRED_ID,INGRED_NAME,STORES) values (3,'FLOUR','Piggly Wiggly');
Insert into SKIP.INGREDIENTS (INGRED_ID,INGRED_NAME,STORES) values (4,'YEAST',null);
Insert into SKIP.INGREDIENTS (INGRED_ID,INGRED_NAME,STORES) values (5,'BEER','ABC Store');
  CREATE TABLE "SKIP"."PRETZELS"
   (     "PRETZEL_ID" NUMBER,
     "PRETZEL_NAME" VARCHAR2(20 BYTE),
     "PRETZEL_DESC" VARCHAR2(100 BYTE)
   ) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
  STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
  TABLESPACE "USERS" ;
REM INSERTING into SKIP.PRETZELS
Insert into SKIP.PRETZELS (PRETZEL_ID,PRETZEL_NAME,PRETZEL_DESC) values (1,'CLASSIC','Classic knot pretzel');
Insert into SKIP.PRETZELS (PRETZEL_ID,PRETZEL_NAME,PRETZEL_DESC) values (2,'THICK STICK','Straight pretzel, abt 1/2" in dia');
  CREATE TABLE "SKIP"."INGRED_XREF"
   (     "PRETZEL_ID" NUMBER,
     "INGRED_ID" NUMBER
   ) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
  STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
  TABLESPACE "USERS" ;
REM INSERTING into SKIP.INGRED_XREF
Insert into SKIP.INGRED_XREF (PRETZEL_ID,INGRED_ID) values (1,1);
Insert into SKIP.INGRED_XREF (PRETZEL_ID,INGRED_ID) values (1,2);
Insert into SKIP.INGRED_XREF (PRETZEL_ID,INGRED_ID) values (1,4);
Insert into SKIP.INGRED_XREF (PRETZEL_ID,INGRED_ID) values (2,2);
Insert into SKIP.INGRED_XREF (PRETZEL_ID,INGRED_ID) values (2,3);
Insert into SKIP.INGRED_XREF (PRETZEL_ID,INGRED_ID) values (2,5);
--  Constraints for Table INGRED_XREF
  ALTER TABLE "SKIP"."INGRED_XREF" MODIFY ("PRETZEL_ID" NOT NULL ENABLE);
  ALTER TABLE "SKIP"."INGRED_XREF" MODIFY ("INGRED_ID" NOT NULL ENABLE);
{code}
Desired output (note how the ingredients are all listed in one column, separated by commas):
{code}
PRETZEL_ID PRETZEL_NAME     PRETZEL_DESC                        INGREDIENTS
1          CLASSIC          Classic knot pretzel                SEA SALT, TABLE SALT, YEAST
2          THICK STICK      Straight pretzel, abt 1/2" in dia   TABLE_SALT, FLOUR, BEER

Answer 1

See the FAQ : {message:id=9360005}
Especially links concerning string aggregation.