Question

我遇到了EXISTS子句无法正常运行的查询。该查询甚至返回不存在匹配记录的项目的结果，似乎完全忽略了EXISTS。它过去运行正常，我认为麻烦是从Oracle 12.1升级到12.2后开始的。

下面是完整的查询（仅更改了表和列的名称以使它们更易读，但我保留了所有逻辑以防与之相关）：

WITH FirstDateFilter AS (
    SELECT ReferenceDate,
           Type,
           LAG(Type, 1, 0) OVER (ORDER BY ReferenceDate) AS PreviousType
    FROM ReferenceDateTable
    WHERE ItemId = :itemId
    AND   ReferenceDate <= :endDate
    AND   Type IN (:type1, :type2)
), SecondDateFilter AS (
    SELECT ReferenceDate
    FROM FirstDateFilter
    WHERE ReferenceDate >= :startDate
    AND   ReferenceDate >= ( SELECT StartDate FROM StartDateTable WHERE ItemId = :itemId )
    AND   Type = :type1
    AND   PreviousType = :type1
)
SELECT ReferenceDate, Value
FROM ResultTable
WHERE ItemId = :itemId
AND EXISTS ( SELECT * FROM SecondDateFilter WHERE SecondDateFilter.ReferenceDate = ResultTable.ReferenceDate )

在处理了一些测试数据之后，我认为导致失败的（部分？）行是第二个WITH中的子查询AND ReferenceDate >= ( SELECT StartDate FROM StartDateTable WHERE ItemId = :itemId )。

我发现以下任何修改都会导致EXISTS再次按预期工作：

使用SecondDateFilter加入ResultTable（在ReferenceDate上）
将( SELECT ReferenceDate FROM SecondDateFilter WHERE SecondDateFilter.ReferenceDate = ResultTable.ReferenceDate )放入SELECT ... FROM ResultTable
注释掉StartDateTable子查询（不再对该表进行过滤，但否则它将再次起作用）
将StartDateTable子查询移至第一个WITH

最后一个解决方案实际上解决了该查询的问题（技术上不一样，但是底层的业务逻辑检查出结果始终是相同的），但是我想知道EXISTS子句是否存在一般性问题（应该仅在Oracle 12.2中有效？）我应该注意。我还有很多查询可以利用它。

下面是一个复制错误的测试脚本。下面的查询按预期返回2行，但是删除注释行将得到5行。

CREATE TABLE ReferenceDateTable 
    (
     ItemId number,
     ReferenceDate date, 
     Type varchar2(1)
    ); 
INSERT INTO ReferenceDateTable (ItemId, ReferenceDate, Type) VALUES (1, to_date('19000201', 'YYYYMMDD'), '1');
INSERT INTO ReferenceDateTable (ItemId, ReferenceDate, Type) VALUES (1, to_date('19000202', 'YYYYMMDD'), '1');
INSERT INTO ReferenceDateTable (ItemId, ReferenceDate, Type) VALUES (1, to_date('19000203', 'YYYYMMDD'), '2');
INSERT INTO ReferenceDateTable (ItemId, ReferenceDate, Type) VALUES (1, to_date('19000204', 'YYYYMMDD'), '1');
INSERT INTO ReferenceDateTable (ItemId, ReferenceDate, Type) VALUES (1, to_date('19000205', 'YYYYMMDD'), '1');

CREATE TABLE ResultTable 
    (
     ItemId number,
     ReferenceDate date, 
     Value number
    ); 
INSERT INTO ResultTable (ItemId, ReferenceDate, Value) VALUES (1, to_date('19000201', 'YYYYMMDD'), 1);
INSERT INTO ResultTable (ItemId, ReferenceDate, Value) VALUES (1, to_date('19000202', 'YYYYMMDD'), 2);
INSERT INTO ResultTable (ItemId, ReferenceDate, Value) VALUES (1, to_date('19000203', 'YYYYMMDD'), 3);
INSERT INTO ResultTable (ItemId, ReferenceDate, Value) VALUES (1, to_date('19000204', 'YYYYMMDD'), 4);
INSERT INTO ResultTable (ItemId, ReferenceDate, Value) VALUES (1, to_date('19000205', 'YYYYMMDD'), 5);

CREATE TABLE StartDateTable
    (
     ItemId number,
     StartDate date
    ); 
INSERT INTO StartDateTable (ItemId, StartDate) VALUES (1, to_date('19000101', 'YYYYMMDD'));

WITH FirstDateFilter AS (
    SELECT ReferenceDate,
           Type,
           LAG(Type, 1, 0) OVER (ORDER BY ReferenceDate) AS PreviousType
    FROM ReferenceDateTable
    WHERE ItemId = 1
    AND   ReferenceDate <= to_date('19000205', 'YYYYMMDD')
    AND   Type IN ('1', '2')
), SecondDateFilter AS (
    SELECT ReferenceDate
    FROM FirstDateFilter
    WHERE ReferenceDate >= to_date('19000201', 'YYYYMMDD')
    --AND   ReferenceDate >= ( SELECT StartDate FROM StartDateTable WHERE ItemId = 1 )
    AND   Type = '1'
    AND   PreviousType = '1'
)
SELECT ReferenceDate, Value
FROM ResultTable
WHERE ItemId = 1
AND EXISTS ( SELECT * FROM SecondDateFilter WHERE SecondDateFilter.ReferenceDate = ResultTable.ReferenceDate )
;

Answer 1

根据Jonathan's comments over on Twitter，建议的解决方法是在外部存在子查询中使用unnest提示，因为该问题是由错误（可能是错误28319114）引起的。

[...]
SELECT ReferenceDate, Value
FROM ResultTable
WHERE ItemId = 1
AND EXISTS ( SELECT /*+ UNNEST */ * FROM SecondDateFilter WHERE SecondDateFilter.ReferenceDate = ResultTable.ReferenceDate )

EXISTS无法在WITH子句

1 个答案: