Question

我正在尝试构建一个看起来像这样的视图：

CREATE OR REPLACE VIEW TestView AS 
SELECT 
p.name, 
?? (select count(*)  from Test t where t.currentstate in ('Running', 'Ended') and t.ref = p.key) as HasValues
from ParentTable p

如果当前状态的计数为＆gt;，我希望列HasValues为1或0。 0

有人能告诉我怎么做吗？感谢

Answer 1

CREATE OR REPLACE VIEW TestView AS 
SELECT 
p.name, 
case
  when nvl(t.mycount,0) > 0 then '1'
  else '0'
end HasValues
from ParentTable p
left outer join (select ref, count(*) mycount from Test group by ref) t on t.ref = p.key

Answer 2

如果您在测试表中对于父表中的每一行都有很多行，并且测试表上的连接键已编制索引，那么将查询构造为以下内容可能是最有效的：

CREATE OR REPLACE VIEW TestView AS 
SELECT 
  p.name, 
  (select count(*) 
   from   Test t
   where  t.currentstate in ('Running', 'Ended') and
          t.ref  = p.key and
          rownum = 1) as HasValues
   from ParentTable p;

此查询的HasValues始终为0或1。

如果test和父表之间的行比率小于约10：1 和我想为父表中的所有行运行它，那么我只是加入这两个表像StevieG的回答一样

Answer 3

    -- This has the added advantage that it doesn't count all records,
    -- it only needs to see one.
    CREATE OR REPLACE VIEW testview
    AS
       SELECT p.name
            , CASE
                 WHEN EXISTS
                         (SELECT NULL
                            FROM test t
                           WHERE t.currentstate IN ('Running', 'Ended')
                             AND t.REF = p.key)
                 THEN
                    1
                 ELSE
                    0
              END
                 hasvalues
         FROM parenttable p

如果count＆gt; Oracle SQL查看列值为1 ñ

3 个答案: