Concatenated field conversion error when executing a view in Oracle - html

Question

I have a view (DB_ADMIN.VW_DBA_MONITOR_CURRENTLYEXEC) to be able to visualize the transactions in Oracle. This view makes use of those already existing in the system: v$sql, V$SQLSTATS, v$sqlarea and gv$process.
And the structure and type of columns was as follows:
I have a procedure that attempts to use such a view, format the output to a single HTML string under certain conditions, and send it via email. Here is a simple summary of that procedure:
DECLARE
V_BODY_TEXT CLOB;
BEGIN
select utl_i18n.unescape_reference(xmlagg(xmlelement(e,'
<tr>
<td>' || ltrim(rtrim(TO_CLOB(SID))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(SQL_ID))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(USERNAME))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(ONAME))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(MACHINE))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(WAIT_CLASS))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(EVENT))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(MODULE))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(LOGON_TIME))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(START_TIME))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(TIME))) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(SQL_TEXT))) || '</th>
</tr>
','').extract('//text()')).getclobval()) x
INTO V_BODY_TEXT
FROM DB_ADMIN.VW_DBA_MONITOR_CURRENTLYEXEC WHERE "TIME" > 300;
END;
The error presented by the execution of the above code is because the concatenated result only admits 4000 characters and it doesn't matter if I try to cast (TO_CLOB) field by field or the entire concatenated string, I still get the same error every time. result size is exceeded:
About the above code, the use of the TO_CLOB function, is my last attempt to try to solve the problem.
Said error does not allow any "substring" or "len" type action to be applied to it either.
I've also tried creating a table with all the fields of type CLOB, then inserting the result of the view, and using the above procedure now with the table, but I keep getting the same error every time the generated html code exceeds 4000 characters.
Therefore, I go to this community to see what other options they give me to get out of the problem.

Answer 1

The xmlelement function only accepts up to 4000 characters if the initialization parameter MAX_STRING_SIZE = STANDARD, and 32767 characters if MAX_STRING_SIZE = EXTENDED, so there's no point in converting to CLOB that early in your process. See here.
Also, the utl_i18n.unescape_reference function only accepts VARCHAR2 input, not CLOB. See here. This is the most likely place your query is failing.
Try this, working exclusively with VARCHAR2, doing explicit conversions from NUMBER and DATE types, and saving the aggregation into the largest string to the very end:
DECLARE
V_BODY_TEXT CLOB;
BEGIN
select xmlagg(utl_i18n.unescape_reference(xmlelement(e,'
<tr>
<td>' || TO_CHAR(SID) || '</th>
<td>' || ltrim(rtrim(SQL_ID)) || '</th>
<td>' || ltrim(rtrim(USERNAME)) || '</th>
<td>' || ltrim(rtrim(ONAME)) || '</th>
<td>' || ltrim(rtrim(MACHINE)) || '</th>
<td>' || ltrim(rtrim(WAIT_CLASS)) || '</th>
<td>' || ltrim(rtrim(EVENT)) || '</th>
<td>' || ltrim(rtrim(MODULE)) || '</th>
<td>' || TO_CHAR(LOGON_TIME,'DD-MON-YYYY') || '</th>
<td>' || TO_CHAR(START_TIME,'DD-MON-YYYY') || '</th>
<td>' || TO_CHAR(TIME) || '</th>
<td>' || ltrim(rtrim(TO_CLOB(SQL_TEXT))) || '</th>
</tr>
',''))) x
INTO V_BODY_TEXT
FROM DB_ADMIN.VW_DBA_MONITOR_CURRENTLYEXEC WHERE "TIME" > 300;
END;

Answer 2

XMLType methods are deprecated since Oracle 11gr2, use modern (though, it's hard to tell about XML) SQL functions to access XML data without additional serialization/deserialization issues:
XMLQUERY for extraction.
XMLCAST for deserialization. It does decoding of HTML/XML stuff like & etc to their text values.
Below is an example of three characters padded with zeroes up to 5000 bytes (so resulting in too large value for varchar2)
with t(col) as (
select
xmlelement(e,
to_clob(rpad('<>&', 4000, '0'))
|| to_clob(rpad('0', 1000, '0'))
)
from dual
)
, deser as (
select
xmlcast(xmlquery(
'//text()'
passing col
returning content
) as clob) as res
from t
)
select
length(res),
trim(trailing '0' from res) as res
from deser
LENGTH(RES)
RES
5000
<>&
fiddle
However, you may avoid concatenation at all and serialize SQL result directly into XML with dbms_xmlgen package. Below is an example:
with function f_get_html(
p_rows int
)
return clob
as
l_ctx number;
l_cursor sys_refcursor;
l_res clob;
begin
/* Cursor object is used to be able to use parameters for statement.
In case of static statement may be replaced by string literal
containing SQL statement directly in newcontext call
*/
open l_cursor for
select
dummy as "td", level as "td",
'<>&' as "td"
from dual
connect by level < p_rows
;
/*Use context to set row tags to <tr>*/
l_ctx := dbms_xmlgen.newcontext(
l_cursor
);
dbms_xmlgen.setrowtag(l_ctx, 'tr');
/*Extract content as HTML-formatted clob*/
select xmlserialize(content xmlquery(
'/ROWSET/*'
passing dbms_xmlgen.getxmltype(l_ctx)
returning content
) as clob)
into l_res
from dual;
return l_res;
end;
select f_get_html(4) as res_html
from dual
RES_HTML
<tr><td>X</td><td>1</td><td><>&</td></tr><tr><td>X</td><td>2</td><td><>&</td></tr><tr><td>X</td><td>3</td><td><>&</td></tr>
fiddle

Answer 3

Finally, the solution I found to avoid the various restrictions of the functions used to generate xml code or converters like the utl_i18n.unescape_reference function, was to use a loop with FOR:
DECLARE
V_BODY CLOB;
V_TABLE_BODY CLOB := NULL;
BEGIN
--> DataSource:
FOR r IN (
SELECT SID,
SQL_ID,
USERNAME,
ONAME,
MACHINE,
WAIT_CLASS,
EVENT,
MODULE,
LOGON_TIME,
START_TIME,
TIME,
SQL_TEXT
FROM DB_ADMIN.VW_DBA_MONITOR_CURRENTLYEXEC
WHERE "TIME" > 300
)
LOOP
--> Table Body:
V_TABLE_BODY := V_TABLE_BODY ||
'<tr>'||
'<td>'||trim(r.SID)||'</td>' ||
'<td>'||trim(r.SQL_ID)||'</td>' ||
'<td>'||trim(r.USERNAME)||'</td>' ||
'<td>'||trim(r.ONAME)||'</td>' ||
'<td>'||trim(r.MACHINE)||'</td>' ||
'<td>'||trim(r.WAIT_CLASS)||'</td>' ||
'<td>'||trim(r.EVENT)||'</td>' ||
'<td>'||trim(r.MODULE)||'</td>' ||
'<td>'||trim(r.LOGON_TIME)||'</td>' ||
'<td>'||trim(r.START_TIME)||'</td>' ||
'<td>'||trim(r.TIME)||'</td>' ||
'<td>'||trim(r.SQL_TEXT)||'</td>' ||
'</tr>';
END LOOP;
----
IF V_TABLE_BODY IS NOT NULL THEN
--> HTML Body:
V_BODY :=
'
<body>
<table border="1">
<tr>
<th>SID</th>
<th>SQL_ID</th>
<th>USERNAME</th>
<th>ONAME</th>
<th>MACHINE</th>
<th>WAIT_CLASS</th>
<th>EVENT</th>
<th>MODULE</th>
<th>LOGON_TIME</th>
<th>START_TIME</th>
<th>TIME</th>
<th>SQL_TEXT</th>
</tr>' ||
V_TABLE_BODY || --> Table Body
'</table>
</body>
';
-- Send Mail:
DB_ADMIN.USP_SEND_MAIL(V_BODY); --> Referential
END IF;