Question

是否有更好的（更有效的）方式来进行此查询？

我不想在同一个查询(SELECT PDATA1 ...)

中搜索两次

SELECT package_ID
FROM t_package
WHERE parent_ID IN (SELECT PDATA1
                    FROM t_object
                    WHERE stereotype = 'Process' AND object_type = 'Package')
OR package_ID IN (SELECT PDATA1
                  FROM t_object
                  WHERE stereotype = 'Process' AND object_type = 'Package')

Answer 1

我相信这可以在没有子查询的情况下完成。

SELECT
    DISTINCT(tp.package_ID)
FROM 
    t_package tp
INNER JOIN
    t_object tobj ON tobj.PDATA1 = tp.parent_ID OR tobj.PDATA1 = tp.package_ID
WHERE
    tobj.stereotype = 'Process' AND tobj.object_type = 'Package'

Answer 2

使用EXISTS，像这样 -

SELECT package_ID
FROM t_package t
WHERE exists(SELECT *                        
FROM t_object o
    WHERE stereotype = 'Process'
    AND object_type = 'Package' 
    and (o.PDATA1=t.parent_ID 
    OR  o.PDATA1=t.package_ID)
)

Answer 3

您可以两次加入t_object表;一次查找parent_ID关系，另一次查找package_ID关系。

SELECT p.package_ID
FROM t_package p
LEFT JOIN t_object oParent
ON p.parent_ID = oParent.PDATA1
AND oParent.stereotype = 'Process' 
AND oParent.object_type = 'Package'
LEFT JOIN t_object oPackage
ON p.parent_ID = oParent.PDATA1
AND oPackage.stereotype = 'Process' 
AND oPackage.object_type = 'Package'
WHERE oParent.PDATA1 IS NOT NULL OR oPackage.PDATA1 IS NOT NULL

Answer 4

这真的取决于dbms。有些dbms在EXISTS子句上的执行计划比在IN子句上更好。

通常情况下，简单的联接是最好的。我不太喜欢这个解决方案，因为你的陈述更容易阅读，但关于速度，你可以尝试一下：

select distinct p.package_id
from t_package p
inner join t_object o on o.pdata1 in (p.package_id, p.parent_id)
  and o.stereotype = 'process' and o.object_type = 'package';

在您的情况下，您在t_object表中已有一些ID，其他必须从t_package获取。所以你也可以在这里尝试UNION。它可能更快，但我没有发现这种可能性。它取决于dbms，数据，索引等。

select package_id
from t_package
where parent_id in 
(
  select pdata1
  from t_object
  where stereotype = 'process' and object_type = 'package'
)
union
select pdata1
from t_object
where stereotype = 'process' and object_type = 'package';

或存在：

select package_id
from t_package
where exists
(
  select *
  from t_object
  where pdata1 = parent_id and stereotype = 'process' and object_type = 'package'
)
union
select pdata1
from t_object
where stereotype = 'process' and object_type = 'package';

Answer 5

怎么样：

SELECT package_ID
FROM t_package, t_object
WHERE  stereotype = 'Process' AND object_type = 'Package'
and parent_ID = PDATA1
or package_ID = PDATA1

改进查询有两个where in in子句

5 个答案: