结合三个SELECT语句时遇到问题，UNION不工作

Question

将三个select语句组合在一起时遇到了很大的麻烦，我尝试过union不起作用，因为它们可以工作的单独select语句但是我需要将其余部分作为一个swift语句，if可能的，即使把最后的记录以随机顺序

 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在每个查询，那么试试这个：

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

为了对部分查询使用ORDER BY子句，而总体而言，使用括号：

(
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 
)