mysql - 组合三个 SELECT 语句时出现问题，UNION 不起作用

Question

我在组合三个选择语句时遇到了巨大的麻烦，我尝试过联合它不起作用，因为单独的选择语句它们确实有效，但是我需要其余的成为一个快速语句，如果可能的话，甚至将最终记录随机放入订单

      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

如果您在每个查询中都需要 ORDER BY，请尝试以下操作:

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