結合三個SELECT語句時遇到問題，UNION不工作

Question

將三個select語句組合在一起時遇到了很大的麻煩，我嘗試過union不起作用，因爲它們可以工作的單獨select語句但是我需要將其餘部分作爲一個swift語句，if可能的，即使把最後的記錄以隨機順序

 SELECT DISTINCT email 
     FROM customer_1_tbl 
     WHERE email NOT IN (SELECT temp.email 
          FROM temp_emails AS temp) 
     AND substring_index(email, '@', -1) = 'seznam.cz' 
     ORDER BY RAND() 
     LIMIT 6 

     UNION 

     SELECT DISTINCT email 
     FROM customer_1_tbl 
     WHERE email NOT IN (SELECT temp.email 
          FROM temp_emails AS temp)  
     AND substring_index(email, '@', -1) = 'gmail.com' 
     ORDER BY RAND() 
     LIMIT 6 

     UNION 

     SELECT DISTINCT email 
     FROM customer_1_tbl 
     WHERE email NOT IN (SELECT temp.email 
          FROM temp_emails AS temp) 
     AND substring_index(email, '@', -1) != 'gmail.com' 
     AND substring_index(email, '@', -1) != 'seznam.cz' 
     AND RAND() < (SELECT ((6/COUNT(*))*10) 
         FROM customer_1_tbl) 
     ORDER BY RAND() 
     LIMIT 6 

Answer 1

如果需要ORDER BY在每個查詢，那麼試試這個：

SELECT * FROM(
    SELECT DISTINCT email 
    FROM customer_1_tbl 
    WHERE email NOT IN (SELECT temp.email 
             FROM temp_emails AS temp) 
    AND substring_index(email, '@', -1) = 'seznam.cz' 
    ORDER BY RAND() 
    LIMIT 6 
) AS A 

UNION 

SELECT * FROM (
    SELECT DISTINCT email 
    FROM customer_1_tbl 
    WHERE email NOT IN (SELECT temp.email 
             FROM temp_emails AS temp)  
    AND substring_index(email, '@', -1) = 'gmail.com' 
    ORDER BY RAND() 
    LIMIT 6 
) AS B 

UNION 
SELECT * FROM (
    SELECT DISTINCT email 
    FROM customer_1_tbl 
    WHERE email NOT IN (SELECT temp.email 
             FROM temp_emails AS temp) 
    AND substring_index(email, '@', -1) != 'gmail.com' 
    AND substring_index(email, '@', -1) != 'seznam.cz' 
    AND RAND() < (SELECT ((6/COUNT(*))*10) 
           FROM customer_1_tbl) 
    ORDER BY RAND() 
    LIMIT 6 
) AS C 

Answer 2

爲了對部分查詢使用ORDER BY子句，而總體而言，使用括號：

(
SELECT DISTINCT email 
    FROM customer_1_tbl 
    WHERE email NOT IN (SELECT temp.email 
         FROM temp_emails AS temp) 
    AND substring_index(email, '@', -1) = 'seznam.cz' 
    ORDER BY RAND() 
    LIMIT 6 
) 
    UNION 
(
    SELECT DISTINCT email 
    FROM customer_1_tbl 
    WHERE email NOT IN (SELECT temp.email 
         FROM temp_emails AS temp)  
    AND substring_index(email, '@', -1) = 'gmail.com' 
    ORDER BY RAND() 
    LIMIT 6 
) 
    UNION 
(
    SELECT DISTINCT email 
    FROM customer_1_tbl 
    WHERE email NOT IN (SELECT temp.email 
         FROM temp_emails AS temp) 
    AND substring_index(email, '@', -1) != 'gmail.com' 
    AND substring_index(email, '@', -1) != 'seznam.cz' 
    AND RAND() < (SELECT ((6/COUNT(*))*10) 
        FROM customer_1_tbl) 
    ORDER BY RAND() 
    LIMIT 6 
)