Question

I’m using Oracle 11g r2 and I need to concatenate strings (VARCHAR2, 300) from multiple rows. I’m using LISTAGG which works great until the concatenated string reaches the limit. At that point I receive a ORA-01489: result of string concatenation is too long.

In the end, I only want the first 4000 chars of the concatenated string. How I get there doesn’t matter. I will accept inefficient solutions.

Here’s my query:

SELECT LISTAGG(T.NAME, ' ') WITHIN GROUP (ORDER BY NULL)
FROM T

Answer 1

You can either use the built-in (but deprecated) STRAGG function

    select sys.stragg(distinct name) from t

(please note that distinct seems to be necessary to avoid duplicates)

or define your own aggregation function / type:

CREATE OR REPLACE TYPE "STRING_AGG_TYPE" as object
(
  total varchar2(4000),

  static function ODCIAggregateInitialize(sctx IN OUT string_agg_type) return number,

  member function ODCIAggregateIterate(self  IN OUT string_agg_type,
                                       value IN varchar2) return number,

  member function ODCIAggregateTerminate(self        IN string_agg_type,
                                         returnValue OUT varchar2,
                                         flags       IN number) return number,

  member function ODCIAggregateMerge(self IN OUT string_agg_type,
                                     ctx2 IN string_agg_type) return number
);

CREATE OR REPLACE TYPE BODY "STRING_AGG_TYPE" is

  static function ODCIAggregateInitialize(sctx IN OUT string_agg_type) return number is
  begin
    sctx := string_agg_type(null);
    return ODCIConst.Success;
  end;

  member function ODCIAggregateIterate(self  IN OUT string_agg_type,
                                       value IN varchar2) return number is
  begin
    -- prevent buffer overflow for more than 4,000 characters
    if nvl(length(self.total),
           0) + nvl(length(value),
                    0) < 4000 then
      self.total := self.total || ';' || value;
    end if;
    return ODCIConst.Success;
  end;

  member function ODCIAggregateTerminate(self        IN string_agg_type,
                                         returnValue OUT varchar2,
                                         flags       IN number) return number is
  begin
    returnValue := ltrim(self.total,
                         ';');
    return ODCIConst.Success;
  end;

  member function ODCIAggregateMerge(self IN OUT string_agg_type,
                                     ctx2 IN string_agg_type) return number is
  begin
    self.total := self.total || ctx2.total;
    return ODCIConst.Success;
  end;

end;

CREATE OR REPLACE FUNCTION stragg(input varchar2 )
   RETURN varchar2
   PARALLEL_ENABLE AGGREGATE USING string_agg_type;

and use it like this:

select STRAGG(name) from t

I believe this approach was orginally proposed by Tom Kyte (at least, that’s where I got it from – Asktom: StringAgg