dynamic pivot SQL Query in DB2

I have table like below in DB2 where all these 3 columns are VARCHAR data type

DATE_F    FILE_NM   ROW_ID  COLUMN_NM   COLUMN_VAL 
20200131  ABC.TXT     1      ABC_COL1     123
20200131  ABC.TXT     1      ABC_COL2     XYZ
20201231  ABC.TXT     2      ABC_COL1     456
20201231  ABC.TXT     2      ABC_COL2     XY1
20200630  XYZ.TXT     1      XYZ_COL1     PQR
20200630  XYZ.TXT     1      XYZ_COL2     567
20200630  XYZ.TXT     1      XYZ_COL3     MNO

I need a dynamic PIVOT query which should select values for ABC_COL1 and ABC_COL2 in row format when FILE_NM filter is used as ABC.TXT

The same query should select the values for XYZ_COL1, XYZ_COL2 and XYZ_COL3 in row format when FILE_NM filter is used as XYZ.TXT

output should be like below when FILE_NM=ABC.TXT

DATE_F    ROW_ID   ABC_COL1   ABC_COL2    
20200131    1        123       XYZ
20201231    2        456       XY1

output should be like below when FILE_NM=XYZ.TXT

 DATE_F    ROW_ID     XYZ_COL1     XYZ_COL2     XYZ_COL3
20200630    1           PQR         567           MNO

So, one one query will be able to extract the data. Can any function or equivalent can do the task in this case ?

Answer

You may try the following generic Stored Procedure doing pivoting.

--#SET TERMINATOR @
create or replace procedure pivot
(
  in  sel_stmt varchar(4000)
, in  row_cols varchar(200)
, in  col_col  varchar(128)
, in  agg_col  varchar(128)
, in  agg_fn   varchar(10)
, in  tmp_tbl  varchar(128)
, in  null_ind varchar(10)
, out rc       int
, out msg      varchar(128)
, out stmt     varchar(4000)
)
LANGUAGE SQL
DYNAMIC RESULT sets 1
BEGIN
 declare QUOT1        char(1) default '''';
 declare QUOT2        char(1) default '"';
 declare SQLCODE      int default 0;
 declare SQLTYPE_ID   int;
 declare SQLTYPE      varchar(128);
 declare SQLLENGTH    int;
 declare SQLSCALE     int;
 declare SQLNAME_DATA varchar(128);
 declare SQLTYPEF     varchar(128);
 declare col_val      varchar(4000);
 declare apo          varchar(1);
 declare l1 RESULT_set_LOCATOR VARYING;

 declare c2 cursor for s2;
 declare c_out cursor with return for s_out;

 declare EXIT HANDLER FOR SQLEXCEPTION
 BEGIN
   GET DIAGNOSTICS EXCEPTION 1 MSG = MESSAGE_TEXT;
   set RC = SQLCODE;
 END;

 set col_col=upper(col_col);
 set agg_col=upper(agg_col);
 -- insert result of select statement into temp table
 set stmt = 'describe '||sel_stmt;
 call SYSPROC.ADMIN_CMD(stmt);
 set stmt = '';
 associate result set locator (l1)
 with procedure SYSPROC.ADMIN_CMD;
 allocate c1 cursor for result set l1;
 --open c1;
 fetch c1 into SQLTYPE_ID, SQLTYPE, SQLLENGTH, SQLSCALE, SQLNAME_DATA;
 while (SQLCODE!=100) do
   set SQLTYPEF = SQLTYPE
   ||case 
      when SQLTYPE IN ('DECIMAL', 'DECFLOAT', 'CHARACTER', 'VARCHAR') then 
         '('||RTRIM(CHAR(SQLLENGTH))
       ||case when SQLTYPE='DECIMAL' then ','||RTRIM(CHAR(SQLSCALE)) else '' end
       ||')'                                
      else ''
     end;
   if (col_col=SQLNAME_DATA) then
     set apo = 
      case 
       when SQLTYPE in ('DECIMAL', 'DECFLOAT', 'INTEGER', 'SMALLINT', 'BIGINT', 'REAL', 'DOUBLE') then '' 
       else QUOT1 
      end;
   end if;
   set stmt = stmt||', '||SQLNAME_DATA||' '||SQLTYPEF;
   fetch c1 into SQLTYPE_ID, SQLTYPE, SQLLENGTH, SQLSCALE, SQLNAME_DATA;
 end while;
 close c1;
 set stmt = 
   'declare global temporary table '||tmp_tbl||'('||substr(stmt, 3)
 ||') with replace on commit preserve rows not logged';
 execute immediate stmt;
 set stmt = 'insert into '||tmp_tbl||' '||sel_stmt;
 execute immediate stmt;

 -- construct select statement
 set stmt = 'select distinct rtrim(char('||col_col||')) from '||tmp_tbl||' order by 1';
 prepare s2 from stmt;
 set stmt='';
 open c2;
 fetch c2 into col_val;
 while (SQLCODE!=100) do
   set stmt = 
     stmt||', '||agg_fn||'('
   ||'case when '||col_col||' '
   ||case when col_val is null then 'IS NULL' else ('='||apo||replace(col_val, QUOT1, QUOT1||QUOT1)||apo) end
   ||' then '||agg_col||' end) as '||QUOT2||coalesce(replace(col_val, QUOT2, QUOT2||QUOT2), null_ind)||QUOT2;
   fetch c2 into col_val;
 end while;
 close c2;
 -- add to the select statement groups
 set row_cols = nullif(row_cols, '');
 set stmt = 
   'select '||case when row_cols is not null then row_cols||',' else coalesce(row_cols, '') end
 ||substr(stmt, 2)||' from '||tmp_tbl||' '
 ||case when row_cols is not null then ('group by '||row_cols||' order by '||row_cols) else '' end;
 -- execute this statement
 prepare s_out from stmt;
 open c_out;
END@

Parameter description:

PARM	DESC
sel_stmt	Any valid SELECT statement for source data generation
row_cols	Comma separated list of column names used in the GROUP BY of final statement
col_col	A column name to pivot
agg_col	A column name to aggregate
agg_fn	Any valid Db2 aggregation function for the column name in “agg_col” parameter
tmp_tbl	DGTT name for intermediate result
null_ind	Null indicator
rc	Return code (OUT)
msg	Message text (OUT)
stmt	The final SELECT generated (OUT)

Brief description:
DGTT passed in tmp_tbl is created and populated with the result of a SELECT statement passed in sel_stmt. All the column names specified in row_cols, col_col, agg_col must be in the SELECT list of this statement.
The final SELECT statement on this DGTT is dynamically generated using the following rules:

• for each distinct value Vx in the column name passed in col_col an additional column expression is generated like: , <agg_fn> (case when <col_col> = Vx then <agg_col> end) as "Vx" (, <agg_fn> (case when <col_col> IS NULL then <agg_col> end) as "<null_ind>" is used for Vx IS NULL), where <parameter> means string value passed with this parameter.
• row_cols column list is used in the GROUP BY, if it’s not NULL.

Use for your case:

DECLARE GLOBAL TEMPORARY TABLE SESSION.MYTAB 
(DATE_F, FILE_NM, ROW_ID, COLUMN_NM, COLUMN_VAL)
AS
(
VALUES
  ('20200131', 'ABC.TXT', 1, 'ABC_COL1', '123')
, ('20200131', 'ABC.TXT', 1, 'ABC_COL2', 'XYZ')
, ('20201231', 'ABC.TXT', 2, 'ABC_COL1', '456')
, ('20201231', 'ABC.TXT', 2, 'ABC_COL2', 'XY1')
, ('20200630', 'XYZ.TXT', 1, 'XYZ_COL1', 'PQR')
, ('20200630', 'XYZ.TXT', 1, 'XYZ_COL2', '567')
, ('20200630', 'XYZ.TXT', 1, 'XYZ_COL3', 'MNO')
) WITH DATA WITH REPLACE ON COMMIT PRESERVE ROWS NOT LOGGED;

1-st call:

call pivot
(
  'select * from session.mytab where file_nm = ''ABC.TXT'''
, 'DATE_F, ROW_ID'
, 'COLUMN_NM'
, 'COLUMN_VAL'
, 'max'
, 'session.tab1'
, '-'
, ?, ?, ?
);

DATE_F	ROW_ID	ABC_COL1	ABC_COL2
20200131	1	123	XYZ
20201231	2	456	XY1

2-nd call:

call pivot
(
  'select * from session.mytab where file_nm = ''XYZ.TXT'''
, 'DATE_F, ROW_ID'
, 'COLUMN_NM'
, 'COLUMN_VAL'
, 'max'
, 'session.tab1'
, '-'
, ?, ?, ?
);

DATE_F	ROW_ID	XYZ_COL1	XYZ_COL2	XYZ_COL3
20200630	1	PQR	567	MNO