if exists statement between a case when condition sql

问题

In the middle of my stored procedure, I have the following snippet of code:

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

however, the final condition, wherein i have to select from the table Waitlisthousehold, has an issue. Not all databases has that table. so I want that last condition to be included when the table exists. But i'm getting errors when i try to do this:

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

So how do i do it correctly?

This snippet is inside a from statement(from table1 a join table2 b on a.id=b.id and case when..)

回答1:

you can have another case when clause inside your one to check if the table exist or not

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

回答2:

you can't add an if inside the select statement like that. you could do this:

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

来源：https://stackoverflow.com/questions/16074287/if-exists-statement-between-a-case-when-condition-sql

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sql

case