如果count> n，则Oracle SQL View列值1

Question

我试图建立一个应该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

我想将HasValues列设为1或0。如果当前状态的计数大于0，则返回1。

有人可以告诉我该怎么做吗？ 谢谢

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

如果对于父表中的每一行，测试表中可能有很多行，并且索引了测试表上的连接键，则将查询构造为以下方式可能是最有效的：

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;

对于此查询，HasValues将始终为0或1。

如果测试表和父表之间的行比小于10：1， 并且我想对父表中的所有行运行该比率，那么我将按照StevieG的答案将两个表连接在一起

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