SQL - CASE當計數不同的值

Question

我需要顯示每個「ID」有多少個不同的值。

它應該是這樣的：

id | component_a | component_b | component_c 
-------------------------------------------------- 
KLS11 |  none  |  one |  none  
KLS12 |  one  |  one |  none   
KLS13 |  several |  one |  none   
KLS14 |  one  |  one |  one    
KLS15 |  one  | several |  several   

我有如下表（表-A）：

id | component_a | component_b | component_c 
-------------------------------------------------- 
KLS11 |    |  a  |    
KLS12 |  a  |  a  |    
KLS13 |  a  |  a  |    
KLS13 |  b  |  a  |    
KLS14 |  a  |  a  |  a   
KLS15 |  a  |  a  |  a     
KLS15 |  a  |  b  |  b 

下面的例子/解釋：

• KLS13有不同的價值觀component_a（a，b） - 所以它應該顯示'幾個'
• KLS13具有component_b（A，A）相同的值 - 因此它應該顯示 '一個'
• KLS13具有component_c沒有價值 - 因此它應該顯示 '無'

這是我的SQL代碼：

我已經爲component_a做了它，但它不起作用。我究竟做錯了什麼？

SELECT 
CASE WHEN component_a is NULL THEN 'none' 
    WHEN (SELECT count(DISTINCT component_a) 
      FROM table_a 
       WHERE id=(SELECT id 
          FROM table_a GROUP BY id HAVING count(*)>1)>1 THEN 'several' 
    WHEN (SELECT count(DISTINCT component_a) 
      FROM table_a 
       WHERE id=(SELECT id 
          FROM table_a GROUP BY id HAVING count(*)>1)=1 THEN 'one' 
END as componentA 
FROM table_a 

我是一名SQL初學者，所以我將不勝感激任何幫助。

有一個愉快的一天

Answer 1

你得到一個ORA-00936錯誤（我認爲），因爲你是不是每個when分支內關閉括號;因爲子子選擇（與having子句一起）返回多個行，所以沒有相關性，因此添加額外的關閉會將錯誤更改爲'ORA-01427：單行子查詢返回多個行'。

你不需要的子查詢，你只需要統計不同的值作爲case結構的一部分，建立一個searched case expression：

select id, 
    case count(distinct component_a) 
    when 0 then 'none' 
    when 1 then 'one' 
    else 'several' 
    end as component_a 
from table_a 
group by id 
order by id; 

ID COMPONENT_A 
----- ----------- 
KLS11 none   
KLS12 one   
KLS13 several  
KLS14 one   
KLS15 one   

再次爲其他列：

select id, 
    case count(distinct component_a) 
    when 0 then 'none' 
    when 1 then 'one' 
    else 'several' 
    end as component_a, 
    case count(distinct component_b) 
    when 0 then 'none' 
    when 1 then 'one' 
    else 'several' 
    end as component_b, 
    case count(distinct component_c) 
    when 0 then 'none' 
    when 1 then 'one' 
    else 'several' 
    end as component_c 
from table_a 
group by id 
order by id; 

ID COMPONENT_A COMPONENT_B COMPONENT_C 
----- ----------- ----------- ----------- 
KLS11 none  one   none   
KLS12 one   one   none   
KLS13 several  one   none   
KLS14 one   one   one   
KLS15 one   several  several  

Answer 2

嘗試此查詢：

WITH t1 as 
(SELECT COUNT(DISTINCT COMPONENT_A) COMPONENT_A, 
COUNT(DISTINCT COMPONENT_B) COMPONENT_B,COUNT(DISTINCT COMPONENT_C) COMPONENT_C 
FROM TABLE1 GROUP BY ID) 
SELECT 
CASE 
WHEN COMPONENT_A = 1 THEN 'one' 
WHEN COMPONENT_A > 1 THEN 'several' ELSE 'none' END AS COMPONENT_A, 
CASE 
WHEN COMPONENT_B = 1 THEN 'one' 
WHEN COMPONENT_B > 1 THEN 'several' ELSE 'none' END AS COMPONENT_B, 
CASE 
WHEN COMPONENT_C = 1 THEN 'one' 
WHEN COMPONENT_C > 1 THEN 'several' ELSE 'none' END AS COMPONENT_C 
FROM t1;