How can I call a db2 function and have it return multiple xml record data? - sql

Question

In SQL, I need to create xml code that looks like this:
<Phone>
<PhoneTypeCode tc="12">Mobile</PhoneTypeCode>
<Area>801</Area>
<DialNumber>9996666</DialNumber>
</Phone>
<Phone>
<PhoneTypeCode tc="2">Business</PhoneTypeCode>
<Area>801</Area>
<DialNumber>1113333</DialNumber>
</Phone>
When I run this sql, I correctly get two rows of data, as I would expect:
select
xmlelement(
Name "Phone",
xmlelement(
name "PhoneTypeCode",
xmlattributes(
trim(p1.phtype) as "tc"
),
trim(p1.desc)
),
xmlelement(name "AreaCode", p1.area),
xmlelement(name "DialNumber", p1.phone)
) as xml
from phone as p1 where p1.entityid = 256285;
These are the two rows of data I get back, exactly as I expected:
<Phone><PhoneTypeCode tc="12">Mobile</PhoneTypeCode><AreaCode>351</AreaCode> <DialNumber>4443333</DialNumber></Phone>
<Phone><PhoneTypeCode tc="2">Business</PhoneTypeCode><AreaCode>351</AreaCode><DialNumber>3911111</DialNumber></Phone>
However, when I try putting this same code in a function and call this function, I get this error:
SQL State: 21000
Vendor Code: -811
Message: [SQL0811] Result of SELECT more than one row. Cause . . . . . : The result table of a SELECT INTO statement, a subquery, or a subselect of a SET statement contains more than one row. The error type is 2. If the error type is 1 then a SELECT INTO statement attempted to return more than one row. If the error type is 2 then a subselect of a basic predicate has produced more than one row. Only one row is allowed. Recovery . . . : Change the selection so that only one result row is returned and then try the request again. The DECLARE CURSOR, OPEN, and FETCH statements must be used to process more than one result row. For a subquery the IN, EXISTS, ANY or ALL predicates can be used to process more than one result row. If one row was expected, there may be data errors, such as duplicate rows, that are causing more than one row to be returned.
**How can I fix this function so that it will return all rows of data as one block of xml code as I expect?
CREATE or replace FUNCTION xml_entity_phones (
#Entity_ID bigint)
RETURNS xml
LANGUAGE SQL
NOT DETERMINISTIC
reads SQL DATA
RETURNS NULL ON NULL INPUT
NO EXTERNAL ACTION
ALLOW PARALLEL
NOT FENCED
begin
return (
select
xmlelement(
Name "Phone",
xmlelement(
name "PhoneTypeCode",
xmlattributes(
trim(p.phtype) as "tc"
),
trim(p.desc)
),
xmlelement(name "AreaCode", p.area),
xmlelement(name "DialNumber", p.phone)
) as xml
from phone p where p.entityid = #entity_id
);
end
;
The procedure that calls this function, is building an xml file that includes different types of phones, which I wanted to build with the above function.
The end goal is to have an xml document (valid or not) that looks like this:
<TXLife>
<TXLifeRequest>
<OLife>
<Person>
<Phone>
<PhoneTypeCode tc="12">Mobile...
<Area...
<DialNumber...
</Phone>
<Phone>
<PhoneTypeCode tc="2">Business...
<Area...
<DialNumber...
</Phone>
...
I was hoping to build the entire phone section xml with a function call like: xml_entity_phones(bigint(e.entityid)).
OK, I changed the function to look like this with xmlagg():
begin
return (
select
xmlagg(
xmlelement(
Name "Phone",
xmlelement(
name "PhoneTypeCode",
xmlattributes(
trim(p.phtype) as "tc"
),
trim(p.desc)
),
xmlelement(name "AreaCode", p.area),
xmlelement(name "DialNumber", p.phone)
)
) as xml
from phone p
where p.entityid = #entity_id
);
end
But now when I call the function with values(xml_entity_phones(256285));, I get ++++++++++++++ as a result. And when I call the procedure that calls this function, I get this error:
SQL State: 22023
Vendor Code: -802
Message: [SQL0802] Data conversion or data mapping error. Cause . . . . . : Error type 10 has occurred 10 -- User-defined function returned a mapping error.
I did notice that when I include an extra element of Phones using xmlagg as suggested in a couple of answers below, that it does return the xmlagg() result successfully. However I can't have that extra element of Phones because it goes against the standard I need to adhere to.
Is there a way to return the xmlagg without the extra layer?

Answer 1

This is where you would use XMLAGG():
begin
return (
select
xmlelement(name "Phones", xmlagg(
xmlelement(
Name "Phone",
xmlelement(
name "PhoneTypeCode",
xmlattributes(
trim(p.phtype) as "tc"
),
trim(p.desc)
),
xmlelement(name "AreaCode", p.area),
xmlelement(name "DialNumber", p.phone)
)
)) as xml
from phone p where p.entityid = #entity_id
);
end
Obviously, I don't have your data but this simple example shows that the approach works:
$ db2 "create or replace function t () returns xml language sql begin \
return (select xmlagg(xmlelement(name \"tab\", tabname )) from syscat.tables \
where tabname like '%AUTH%' and tabschema = 'SYSCAT'); end"
DB20000I The SQL command completed successfully.
$ db2 "values t()"
1
----------------------------------------------------------------------------
<tab>COLAUTH</tab><tab>DBAUTH</tab><tab>INDEXAUTH</tab><tab>LIBRARYAUTH</tab>
<tab>MODULEAUTH</tab><tab>PACKAGEAUTH</tab><tab>PASSTHRUAUTH</tab><tab>ROLEAUTH
</tab><tab>ROUTINEAUTH</tab><tab>SCHEMAAUTH</tab><tab>SEQUENCEAUTH</tab>tab>
SURROGATEAUTHIDS </tab><tab>TABAUTH</tab><tab>TBSPACEAUTH</tab><tab>
VARIABLEAUTH</tab><tab>WORKLOADAUTH</tab><tab>XSROBJECTAUTH</tab>
1 record(s) selected.

Answer 2

When you issue a SQL select, you are retrieving a resultset (in some way a cursor). What you have is not a XML, it is a resultset that has two XML documents, or two rows. A XML document has just one parent, here you have two parents (phone)
You can retrieve a cursor like the one you have via a Stored Procedure.
create procedure x ()
P1:BEGIN
DECLARE cursor1 CURSOR WITH RETURN TO CLIENT FOR
xmlelement(
Name "Phone",
...
xmlelement(name "DialNumber", p1.phone)
) as xml
from phone as p1 where p1.entityid = 256285;
open cursor1;
END P1;