UNION ALL returning wrong results?

有应用人员反映某套Linux上的11.2.0.1数据库系统中出现了UNION ALL后返回的结果集不正确的问题,我们具体分析下出现问题的其中一条语句:

SELECT MTL_SECONDARY_INVENTORIES.SECONDARY_INVENTORY_NAME,
       MTL_SECONDARY_INVENTORIES.ORGANIZATION_ID,
       MTL_SECONDARY_INVENTORIES.DESCRIPTION,
       MTL_SECONDARY_INVENTORIES.AVAILABILITY_TYPE,
       MTL_SECONDARY_INVENTORIES.MATERIAL_ACCOUNT,
       MTL_SECONDARY_INVENTORIES.MATERIAL_OVERHEAD_ACCOUNT,
       MTL_SECONDARY_INVENTORIES.RESOURCE_ACCOUNT,
       MTL_SECONDARY_INVENTORIES.OVERHEAD_ACCOUNT,
       MTL_SECONDARY_INVENTORIES.OUTSIDE_PROCESSING_ACCOUNT,
       MTL_SECONDARY_INVENTORIES.ASSET_INVENTORY,
       MTL_SECONDARY_INVENTORIES.EXPENSE_ACCOUNT,
       MTL_SECONDARY_INVENTORIES.ENCUMBRANCE_ACCOUNT,
       MTL_SECONDARY_INVENTORIES.ATTRIBUTE3,
       MTL_SECONDARY_INVENTORIES.ATTRIBUTE5,
       WORKFLOW_START_TIMES.WORKFLOW_START_TIME
  FROM REPEMEAERP.MTL_SECONDARY_INVENTORIES,
       REPEMEAERP.WORKFLOW_START_TIMES
 WHERE MTL_SECONDARY_INVENTORIES.DW_UPDATE_DT >
       TO_DATE('01/01/1900 00:00:00', 'MM/DD/YYYY HH24:MI:SS')
   AND MTL_SECONDARY_INVENTORIES.DW_UPDATE_DT <=
       WORKFLOW_START_TIMES.WORKFLOW_START_TIME
   AND WORKFLOW_START_TIMES.WORKFLOW_NAME =
       LTRIM(RTRIM('w_int_FreqBatch_EMEA'))
/*以上是QUERY A*/
UNION ALL
/*以下是QUERY B*/
SELECT DISTINCT 'WORKORDERS',
                MTL_SECONDARY_INVENTORIES.ORGANIZATION_ID,
                'WORK ORDERS WITH WIP AS CATEGORY VALUE',
                1,
                0,
                0,
                0,
                0,
                0,
                1,
                0,
                0,
                'MOI',
                '0',
                WORKFLOW_START_TIMES.WORKFLOW_START_TIME
  FROM REPEMEAERP.MTL_SECONDARY_INVENTORIES, EIMMAINT.WORKFLOW_START_TIMES
 WHERE MTL_SECONDARY_INVENTORIES.DW_UPDATE_DT >
       TO_DATE('01/01/1900 00:00:00', 'MM/DD/YYYY HH24:MI:SS')
   AND MTL_SECONDARY_INVENTORIES.DW_UPDATE_DT <=
       WORKFLOW_START_TIMES.WORKFLOW_START_TIME
   AND WORKFLOW_START_TIMES.WORKFLOW_NAME =
       LTRIM(RTRIM('w_int_FreqBatch_EMEA'))
/
138 rows selected.

以上查询语句中，QUERY A部分(也就是UNION ALL之前的SELECT语句)单独查询时返回返回69条记录，QUERY B部分单独查询时返回15记录，UNION ALL后返回的结果却是138条记录，而非84条记录。实际上这套系统也是最近才从10g迁移到11gr2上，之前在10g中同样的应用没有出过类似的问题，可以猜测是11g中新引入的某种特性存在可能引发wrong result的Bug。 具体思路虽然有了，但仍无法确定问题的关键所在；我们来看看该SQL的执行计划:

-----------------------------------------------------------------------------------------------------------------
| Id  | Operation                       | Name                          | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                |                               |     7 |  2443 |    52   (0)| 00:00:01 |
|   1 |  NESTED LOOPS                   |                               |     7 |  2443 |    52   (0)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL             | WORKFLOW_START_TIMES          |     1 |    29 |    48   (0)| 00:00:01 |
|   3 |   VIEW                          | VW_JF_SET$9BAED2EA            |     1 |   320 |     4   (0)| 00:00:01 |
|   4 |    UNION ALL PUSHED PREDICATE   |                               |       |       |            |          |
|*  5 |     FILTER                      |                               |       |       |            |          |
|   6 |      TABLE ACCESS BY INDEX ROWID| MTL_SECONDARY_INVENTORIES     |     3 |   336 |     2   (0)| 00:00:01 |
|*  7 |       INDEX RANGE SCAN          | IDX_MTL_SECONDARY_INVENTORIES |     1 |       |     1   (0)| 00:00:01 |
|*  8 |     FILTER                      |                               |       |       |            |          |
|   9 |      TABLE ACCESS BY INDEX ROWID| MTL_SECONDARY_INVENTORIES     |     3 |    36 |     2   (0)| 00:00:01 |
|* 10 |       INDEX RANGE SCAN          | IDX_MTL_SECONDARY_INVENTORIES |     1 |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------

2 - filter("WORKFLOW_START_TIMES"."WORKFLOW_NAME"='w_int_FreqBatch_EMEA')
5 - filter(TO_DATE(' 1900-01-01 00:00:00', 'syyyy-mm-dd
hh24:mi:ss')<"WORKFLOW_START_TIMES"."WORKFLOW_START_TIME") 7 - access("MTL_SECONDARY_INVENTORIES"."DW_UPDATE_DT">TO_DATE(' 1900-01-01 00:00:00', 'syyyy-mm-dd
hh24:mi:ss') AND "MTL_SECONDARY_INVENTORIES"."DW_UPDATE_DT"<="WORKFLOW_START_TIMES"."WORKFLOW_START_TIME"
)
8 - filter(TO_DATE(' 1900-01-01 00:00:00', 'syyyy-mm-dd
hh24:mi:ss')<"WORKFLOW_START_TIMES"."WORKFLOW_START_TIME") 10 - access("MTL_SECONDARY_INVENTORIES"."DW_UPDATE_DT">TO_DATE(' 1900-01-01 00:00:00', 'syyyy-mm-dd
hh24:mi:ss') AND "MTL_SECONDARY_INVENTORIES"."DW_UPDATE_DT"<="WORKFLOW_START_TIMES"."WORKFLOW_START_TIME"
)

你可能从以上执行计划中发现了两处十分陌生的字眼:UNION ALL