Question

所以我想要做的就是将行转换为列。以前在本网站上已经涵盖了这种方式，我最喜欢的方式如下：

SELECT 
  FRNPCM032.WFP.WFORD#,
  MAX(CASE WHEN FRNPCM032.WFP.WFSEGN = 'COLOR1'  THEN WFVAL END) AS COLOR,
  MAX(CASE WHEN FRNPCM032.WFP.WFSEGN = 'OSKVA'  THEN WFVAL END) AS KVA,
  MAX(CASE WHEN FRNPCM032.WFP.WFSEGN = 'OSSWITCH'  THEN WFVAL END) AS LBSWITCH
FROM FRNPCM032.WFP
GROUP BY FRNPCM032.WFP.WFORD#;

这是一种非常简单的方法，但是我需要一些不那么手动的东西，因为以后可能会添加新行，我不想再回去继续维护查询或查看。

有没有办法动态地做到这一点？我可以想办法用循环来做，但我不能在查询或视图中这样做。

Answer 1

不幸的是，DB2 for IBM我没有PIVOT（）函数......

但是，您可以构建一个动态查看表的当前内容的过程，并构建一个用于转动数据的SQL语句。

以下代码来自文章An SQL Pivot Procedure

如果您希望可以修改代码来构建视图，而不是返回结果集。但是，如果枢轴值发生变化，您必须重建视图。

CREATE PROCEDURE DO_PIVOT
   (IN FOR_SCHEMA CHARACTER (10) , 
    IN FOR_TABLE CHARACTER (10) , 
    IN PIVOT_COLUMN VARCHAR (250) , 
    IN VALUE_COLUMN VARCHAR (250) , 
    IN AGG_FUNCTION VARCHAR (5) DEFAULT 'SUM' , 
    IN GROUP_COLUMN VARCHAR (250) DEFAULT NULL ) 
    LANGUAGE SQL 
    MODIFIES SQL DATA 
    PROGRAM TYPE SUB 
    CONCURRENT ACCESS RESOLUTION DEFAULT 
    DYNAMIC RESULT SETS 1 
    OLD SAVEPOINT LEVEL COMMIT ON RETURN NO 

BEGIN

   DECLARE SQLCODE INTEGER DEFAULT 0 ;
   DECLARE SQL_STATEMENT VARCHAR ( 5000 ) ;
   DECLARE PIVOT_VALUE VARCHAR ( 20 ) ;
   DECLARE PAD CHAR ( 2 ) DEFAULT ' ' ;

   DECLARE C1 CURSOR FOR D1 ;
   DECLARE C2 CURSOR WITH RETURN FOR D2 ;

   SET SCHEMA = FOR_SCHEMA ;

   -- Get the list of values available for the pivot column
   -- Each value will be a column in the return set
   SET SQL_STATEMENT = 'select distinct ' 
                       || PIVOT_COLUMN  
                       || ' from ' 
                       || FOR_TABLE 
                       || ' order by 1' ;

   PREPARE D1 FROM SQL_STATEMENT ;
   OPEN C1 ;

   -- Construct a dynamic select statement for the pivot
   SET SQL_STATEMENT = 'select ' ;

   -- If requested, add the Group By Column 
   -- to the select clause
   IF GROUP_COLUMN IS NOT NULL THEN
      SET SQL_STATEMENT = SQL_STATEMENT || GROUP_COLUMN ;
      SET PAD = ', ' ;
   END IF ;

   -- For each possible value for the Pivot Column, 
   -- add a case statement to perform the requested 
   -- aggregate function on the Value Column
   FETCH NEXT FROM C1 INTO PIVOT_VALUE ;
   WHILE ( SQLCODE >= 0 AND SQLCODE <> 100 ) DO
      SET SQL_STATEMENT = SQL_STATEMENT 
                          || PAD 
                          || AGG_FUNCTION 
                          || '(CASE WHEN ' 
                          || PIVOT_COLUMN 
                          || ' = ''' 
                          || PIVOT_VALUE 
                          || ''' THEN ' 
                          || VALUE_COLUMN 
                          || '  END) AS ' 
                          || PIVOT_VALUE ;
      SET PAD = ', ' ;
      FETCH NEXT FROM C1 INTO PIVOT_VALUE ;
   END WHILE ;
   CLOSE C1 ;

   -- Specify the table to select from
   SET SQL_STATEMENT = SQL_STATEMENT 
                       || ' from ' 
                       || FOR_TABLE ;

   -- If requested, add the Group By Column
   -- to the select clause
   IF GROUP_COLUMN IS NOT NULL THEN
      SET SQL_STATEMENT = SQL_STATEMENT 
                          || ' group by ' 
                          || GROUP_COLUMN 
                          || ' order by ' 
                          || GROUP_COLUMN;
   END IF ;

   PREPARE D2 FROM SQL_STATEMENT ;
   OPEN C2 ;

END ;

LABEL ON ROUTINE DO_PIVOT 
   ( CHAR(), CHAR(), VARCHAR(), VARCHAR(), VARCHAR(), VARCHAR() )  
   IS 'Perform a General Purpose Pivot';

COMMENT ON PARAMETER ROUTINE DO_PIVOT 
   ( CHAR(), CHAR(), VARCHAR(), VARCHAR(), VARCHAR(), VARCHAR() ) 
   (FOR_SCHEMA IS 'Schema for Table' , 
    FOR_TABLE IS 'For Table' , 
    PIVOT_COLUMN IS 'Name of Column to be Pivoted' , 
    VALUE_COLUMN IS 'Column to be Aggregated for Pivot' , 
    AGG_FUNCTION IS 'Use Aggregate Function' , 
    GROUP_COLUMN IS 'Group on Column' ) ;

动态地在iSeries DB2中透视表

1 个答案: