Why do I get the following error LISTAGG function: “result of string concatenation is too long"?* [duplicate]

问题

I am using this query

HR--Any baby with a HR<80 
AS
(SELECT fm.y_inpatient_dat, h.pat_id, h.pat_enc_csn_id, 
LISTAGG(meas_value, '; ') WITHIN GROUP (ORDER BY fm.recorded_time) abnormal_HR_values
from
ip_flwsht_meas fm
join pat_enc_hsp h on fm.y_inpatient_dat = h.inpatient_data_id
where fm.flo_meas_id in ('8' ) and (to_number(MEAS_VALUE) <'80')
AND fm.recorded_time between (select start_date from dd) AND (select end_date from dd)
group by fm.y_inpatient_dat,h.pat_id, h.pat_enc_csn_id)

and I get the following error:

ORA-01489: result of string concatenation is too long

I have researched online how to set a size limit, but I can't seem to make it work. Can someone please advise how to set a limit so it does not exceed the 50 characters.

回答1:

As other commentators already said, there is no way to avoid such error until Oracle 12.2 (where List_agg has the new option "ON OVERFLOW TRUNCATE").

In previous versions of oracle, if you concatenate strings longer than 4000 bytes, you get that error. you have NO way of preventing it.

If you still need to do that in previous versions, you have to write your own function for doing it and you need to modify your query accordingly:

This custom function might solve your problem

 create or replace type TAB_STRINGS is table of varchar2(4000) 
 /
 create or replace function My_list_agg(strings in TAB_STRINGS,
                      separator  in varchar2,
                      max_len    integer) return varchar2 deterministic is
   result varchar2(32000);
   tmp    varchar2(32000);
 begin
   result := null;
   if strings is not null then
       for idx in strings.first .. strings. last loop
         tmp := strings(idx);
         if tmp is not null then
           if result is null then
             exit when length(tmp) > max_len;
             result := tmp;
           else
             exit when(length(result) + length(separator) + length(tmp)) > max_len;
             result := result || separator || tmp;
           end if;
         end if;
       end loop;
   end if;
   return result;
 end;
 /

you need to use the CAST/COLLECT operator to use it.
this is an usage example:

   select table_name,
          My_list_agg(  
                 -- first argument: array of strings to be concatenated
                 cast ( collect (column_name order by column_name) as TAB_STRINGS),
                 -- second (optional) argument: the separator
                 ',',
                 -- third argument (optional): the maximum length of the string to be returned
                 1000   
          ) as column_list
   from user_tab_columns t
   group by table_name
   order by table_name

来源：https://stackoverflow.com/questions/53029759/why-do-i-get-the-following-error-listagg-function-result-of-string-concatenati

标签

sql

Oracle

oracle11g