The concat() SQL function concatenates two values, so it's just appending the semicolon to each extracted value independently. But you're really trying to do string aggregation of the results (which could, presumably, really be more than two extracted values).
You can use XMLQuery instead of extract, and use an XPath string-join() function to do the concatentation:
XMLQuery('string-join(/A/B, ";")' passing xmltype(a.xml) returning content)
Demo with fixed XMl end-node tags:
-- CTE for sample data
with a (xml) as (
select '<A><B>123</B><C>456</C><B>789</B></A>' from dual
)
-- actual query
select XMLQuery('string-join(/A/B, ";")' passing xmltype(a.xml) returning content) as result
from a;
RESULT
------------------------------
123;789
You could also extract all of the individual <B> values using XMLTable, and then use SQL-level aggregation:
-- CTE for sample data
with a (xml) as (
select '<A><B>123</B><C>456</C><B>789</B></A>' from dual
)
-- actual query
select listagg(x.b, ';') within group (order by null) as result
from a
cross join XMLTable('/A/B' passing xmltype(a.xml) columns b number path '.') x;
RESULT
------------------------------
123;789
which gives you more flexibility and would allow grouping by other node values more easily, but that doesn't seem to be needed here based on your example value.
