预言：案例：I/Elsef查询

Question

我执行SELECT语句如下

Select case 
     when count(*) = 0 then 'Pass' 
     end as Test_Result 
    from Table Name 
where condition; 

我想输出如下

If count(*)=0 then Result should be 'Pass' 

否则我想这个查询的输出。我的意思是下面一个

Select Count(*) 
    from Table Name 
where condition; 

Answer 1

这里的一个选项是没有WHERE条件来执行查询，然后使用条件聚合得到它出现在ELSE条件计数输出。

SELECT CASE WHEN COUNT(*) = 0 THEN 'Pass' 
      ELSE CAST(SUM(CASE WHEN condition THEN 1 ELSE 0 END) AS VARCHAR2(30)) 
     END AS Test_Result 
FROM yourTable 

Answer 2

的一种方法是：

设置：

create table emptyTab (a number); 
create table notEmptyTab (a) as (select 1 from dual); 

这应该做的伎俩：

SQL> select case 
    2   when count(*) = 0 then 'Pass' 
    3   else to_char(count(*)) 
    4   end 
    5 from emptyTab 
    6 where a = 1  ; 

CASEWHENCOUNT(*)=0THEN'PASS'ELSETO_CHAR(
---------------------------------------- 
Pass 

SQL> select case 
    2   when count(*) = 0 then 'Pass' 
    3   else to_char(count(*)) 
    4   end 
    5 from notEmptyTab 
    6 where a = 1; 

CASEWHENCOUNT(*)=0THEN'PASS'ELSETO_CHAR(
---------------------------------------- 
1 

SQL> select case 
    2   when count(*) = 0 then 'Pass' 
    3   else to_char(count(*)) 
    4   end 
    5 from notEmptyTab 
    6 where a = 2; 

CASEWHENCOUNT(*)=0THEN'PASS'ELSETO_CHAR(
---------------------------------------- 
Pass