Case語句值

Question

我需要寫一個case語句將返回

「1 of 3」 if someone voted in one of three elections, 
「2 of 3」 if someone voted in two of three elections, 
「3 of 3」 if someone voted in three of three elections, 

的問題是，某些值是一個varchar，有些是零，我不能把它們加起來。 這是我的想法，但我無法讓它工作。

select 
id, 
CASE 
    WHEN race1 + race2 + race3 = 0 then '0-3' 
    WHEN race1 + race2 + race3 = 1 then '1-3' 
    WHEN race1 + race2 + race3 = 2 then '2-3' 
    WHEN race1 + race2 + race3 = 3 then '3-3' 
    WHEN race1 + race2 + race3 is null then 'Unknown' 
END AS General_Turnout 
from test4 

http://sqlfiddle.com/#!3/cac66/3

Answer 1

這應該工作：

select 
id, 
    CAST((CASE WHEN race1 IS NOT NULL THEN 1 ELSE 0 END) 
    +(CASE WHEN race2 IS NOT NULL THEN 1 ELSE 0 END) 
    +(CASE WHEN race3 IS NOT NULL THEN 1 ELSE 0 END) AS CHAR) + '-3' 
AS General_Turnout 
from test4 

Answer 2

使用COELESCE（數值，0），以便空取爲零

Answer 3

從你貼在SQLfiddle什麼，我想NULL表示未投票，任何字符串表示都投了。你不能添加列中的非數字字符串race1，race2和race3，但這應該工作：

SELECT 
    id, 
    CAST(
    CASE WHEN race1 IS NOT NULL then 1 ELSE 0 END + 
    CASE WHEN race2 IS NOT NULL then 1 ELSE 0 END + 
    CASE WHEN race3 IS NOT NULL then 1 ELSE 0 END 
    AS CHAR) + '-3' AS General_Turnout 
FROM test4