nested group function without GROUP BY

Bonjour,
J'ai une requete qui fonctionne comme attendue, mais lorsque je la mets en format XML, j'ai une erreur qui apparait.
Je pars de cette requète :

Code:

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SELECT NON_CTL_AREA_NAME ,
      (SELECT min(LOWER_LEVEL)
	 	    FROM R_NCA_VO r, VOLUME v					
	 	    WHERE r.AIRSPACE_ENV_NAME=c.AIRSPACE_ENV_NAME
	   	      and v.AIRSPACE_ENV_NAME=r.AIRSPACE_ENV_NAME
	   	      and r.NON_CTL_AREA_NAME=gl.NON_CTL_AREA_NAME#N_C_AREA
	   	      and v.VOLUME_NAME=r.VOLUME_NAME)
FROM N_C_AREA c,GRAPHICAL_LINE_SURF gl
WHERE gl.AIRSPACE_ENV_NAME = c.AIRSPACE_ENV_NAME
  and gl.NON_CTL_AREA_NAME#N_C_AREA = c.NON_CTL_AREA_NAME
  and c.AIRSPACE_ENV_NAME = 'MAASNEW';   
 
NON_CTL_AREA
------------
(SELECTMIN(LOWER_LEVEL)FROMR_NCA_VOR,VOLUMEVWHERER.AIRSPACE_ENV_NAME=C.AIRSPACE_
--------------------------------------------------------------------------------
NORB
                                                                             195

Mis à la sauce XML, cela donne ça :

Code:

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SELECT XMLPARSE(document XMLSERIALIZE(document(
SELECT
XMLELEMENT("ReservedAreaList",
(SELECT XMLAgg(
   XMLELEMENT("ReservedArea",
      XMLELEMENT("ReservedAreaName", NON_CTL_AREA_NAME ),
      (SELECT XMLAgg(
      	  XMLELEMENT("MinFlightLevel",min(LOWER_LEVEL)))
	 	    FROM R_NCA_VO r, VOLUME v					
	 	    WHERE r.AIRSPACE_ENV_NAME=c.AIRSPACE_ENV_NAME
	   	      and v.AIRSPACE_ENV_NAME=r.AIRSPACE_ENV_NAME
	   	      and r.NON_CTL_AREA_NAME=gl.NON_CTL_AREA_NAME#N_C_AREA
	   	      and v.VOLUME_NAME=r.VOLUME_NAME)))
FROM N_C_AREA c,GRAPHICAL_LINE_SURF gl
WHERE gl.AIRSPACE_ENV_NAME = c.AIRSPACE_ENV_NAME
  and gl.NON_CTL_AREA_NAME#N_C_AREA = c.NON_CTL_AREA_NAME
  and c.AIRSPACE_ENV_NAME = 'MAASNEW')
) from dual
))) from dual;

Par contre si j'enlève le min(LOWER_LEVEL), la requète s'exécute :

Code:

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SELECT XMLPARSE(document XMLSERIALIZE(document(
SELECT
XMLELEMENT("ReservedAreaList",
(SELECT XMLAgg(
   XMLELEMENT("ReservedArea",
      XMLELEMENT("ReservedAreaName", NON_CTL_AREA_NAME ),
      (SELECT XMLAgg(
      	  XMLELEMENT("MinFlightLevel",LOWER_LEVEL))
	 	    FROM R_NCA_VO r, VOLUME v					
	 	    WHERE r.AIRSPACE_ENV_NAME=c.AIRSPACE_ENV_NAME
	   	      and v.AIRSPACE_ENV_NAME=r.AIRSPACE_ENV_NAME
	   	      and r.NON_CTL_AREA_NAME=gl.NON_CTL_AREA_NAME#N_C_AREA
	   	      and v.VOLUME_NAME=r.VOLUME_NAME)))
FROM N_C_AREA c,GRAPHICAL_LINE_SURF gl
WHERE gl.AIRSPACE_ENV_NAME = c.AIRSPACE_ENV_NAME
  and gl.NON_CTL_AREA_NAME#N_C_AREA = c.NON_CTL_AREA_NAME
  and c.AIRSPACE_ENV_NAME = 'MAASNEW')
) from dual
))) from dual;	   
 
<ReservedAreaList>
  <ReservedArea>
    <ReservedAreaName>NORB</ReservedAreaName>
    <MinFlightLevel>245</MinFlightLevel>
    <MinFlightLevel>195</MinFlightLevel>
  </ReservedArea>
</ReservedArea

Il ne reste plus qu'à trouver un moyen pour n'avoir que la ligne avec 195 ! Mais cette différence de comportement m'est incompréhensible.

Au cas ou mes tables :

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SQL>  desc graphical_line_surf
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 AIRSPACE_ENV_NAME                         NOT NULL VARCHAR2(20)
 NAME                                      NOT NULL VARCHAR2(6)
 AIRSPACE_ENV_NAME#N_C_AREA                         VARCHAR2(20)
 NON_CTL_AREA_NAME#N_C_AREA                         VARCHAR2(12)
 
SQL> desc n_c_area
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 AIRSPACE_ENV_NAME                         NOT NULL VARCHAR2(20)
 NON_CTL_AREA_NAME                         NOT NULL VARCHAR2(12)
 
SQL> desc r_nca_vo
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 AIRSPACE_ENV_NAME                         NOT NULL VARCHAR2(20)
 NON_CTL_AREA_NAME                         NOT NULL VARCHAR2(12)
 AIRSPACE_ENV_NAME_A                       NOT NULL VARCHAR2(20)
 VOLUME_NAME                               NOT NULL VARCHAR2(20)
 ORDER_NUMBER                                       NUMBER(38)
 
SQL> desc volume
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 AIRSPACE_ENV_NAME                         NOT NULL VARCHAR2(20)
 VOLUME_NAME                               NOT NULL VARCHAR2(20)
 LOWER_LEVEL                               NOT NULL NUMBER(38)
 UPPER_LEVEL                               NOT NULL NUMBER(38)

Merci de votre aide