如果条件sql的case之间存在语句

Question

在我的存储过程中间，我有以下sn-p代码：

case
  when l.codeleasestatuscode = '5' and priorleaseid is null 
  and l.leaid in(select col1 from Waitlisthousehold)
then '2'
else l.codeleasestatuscode
end

但是，我必须从 Waitlisthousehold 表中进行选择的最终条件存在问题。并非所有数据库都有该表。所以我希望在表存在时包含最后一个条件。但是当我尝试这样做时出现错误：

case
when l.codeleasestatuscode = '5' and priorleaseid is null
IF EXISTS(select * from information_schema.tables where table_name='WaitlistHousehold')
  begin
    and l.leaid in(select col1 from Waitlisthousehold)
  end
then '2'
else l.codeleasestatuscode
end

那我该怎么做呢？

这个 sn-p 在 from 语句中（从 table1 a join table2 b on a.id=b.id and case when..）

Answer 1

你可以在你的子句中使用另一种情况来检查表是否存在

CASE
WHEN l.codeleasestatuscode = '5' and priorleaseid is null
    CASE WHEN EXISTS(SELECT * FROM information_schema.tables WHERE table_name='WaitlistHousehold')
        THEN
            CASE WHEN l.leaid in(select col1 from Waitlisthousehold) THEN '2' 
            ELSE l.codeleasestatuscode END
        ELSE '2' END          
    THEN '2'END
ELSE l.codeleasestatuscode
END

Answer 2

你不能像这样在 select 语句中添加 if。你可以这样做：

IF EXISTS(select * from information_schema.tables where table_name='WaitlistHousehold')
  BEGIN
  SELECT whatever,
  case
  when l.codeleasestatuscode = '5' and priorleaseid is null
    and l.leaid in(select col1 from Waitlisthousehold)
  then '2'
  else l.codeleasestatuscode
  end AS whatever1
  FROM wherever
  END
ELSE
  BEGIN
  SELECT whatever,
  case
  when l.codeleasestatuscode = '5' and priorleaseid is null
  then '2'
  else l.codeleasestatuscode
  end AS whatever1
  FROM wherever
  END