php – JOINed表上的GROUP BY和ORDER BY – 复杂而缓慢

故事是这样的……我有用户,他们有孩子.
我想每天使用CRON JOB优惠券向在子女出生日期之间生孩子的用户发送.
我想知道谁将是用户获得优惠券和哪个孩子.
我也想为每个孩子只寄一张优惠券,孩子必须是用户最年轻的.

我有以下表格

Children
+--------------------------------------+
- Primary Key: childrenID (int)
- Index: userID (int)
- Index: childBirthDate (date)
+--------------------------------------+
- childrenID - userID - childBirthDate -
- 1          - 1      - 21/01/2000     -
- 2          - 1      - 01/11/2013     -
- 3          - 1      - 25/10/2013     -
- 4          - 2      - 01/11/2013     -
- 5          - 3      - 01/11/2013     -
+--------------------------------------+

Users
+------------------------+
- Primary Key: userID (int)
- Index: categoryGroup (varchar)
+------------------------+
- userID - categoryGroup -
- 1      - 'Group1'      -
- 2      - 'Group1'      -
- 3      - 'Group2'      -
- 4      - 'Group2'      -
+------------------------+

CuponRequests
+------------------------+
- Primary Key: ID (int)
- Index: userID (int)
- Index: cuponID (int)
+-----------------------+
- ID - cuponID - userID -
- 1  - 1       - 1      -
- 1  - 2       - 1      -
- 1  - 1       - 2      -
+-----------------------+

这基本上是具有相关列的三个主要表
我有以下SQL查询来执行和获取我需要的结果.

SELECT users.userID,users.categoryGroup children.childBirthDate,children.childrenID
FROM users,(SELECT *
   FROM
     (SELECT children.childrenID,children.childBirthDate,users.userID AS child_uid
      FROM children,users
      WHERE children.userID = users.userID
      ORDER BY children.childBirthDate DESC)t1
   GROUP BY child_uid)children
WHERE (children.childBirthDate <= DATE_SUB(CURDATE(),INTERVAL 5 MONTH))
  AND (children.childBirthDate > DATE_SUB(CURDATE(),INTERVAL 6 MONTH))
  AND (children.child_uid = users.userID)
  AND ('Group1,Group2' LIKE CONCAT('%',users.categoryGroup,'%'))
  AND NOT EXISTS
    (SELECT userID,cuponID
     FROM cuponRequests
     WHERE userID = users.userID
       AND cuponID = 1)
  AND userID = 1
ORDER BY children.childBirthDate DESC

对于此查询,我尝试仅在一个用户和一个优惠券上工作
但它的自然行为 – 查询正在对所有用户起作用

“cuponID”和间隔来自脚本的PHP端 – 我迭代“cupons”表(这里没有提到)并在每个“优惠券”行上执行此查询)

问题是此查询正在执行约1.5秒(O.O)
除了在CRON JOB环境中运行此脚本之外,此脚本也会在用户注册到网站后立即运行.我有96个杯子 – 这使得注册速度减慢了大约一分钟(这很多)

我想通了这个查询

SELECT *
FROM
  (SELECT children.childrenID,users.userID AS child_uid
   FROM children,users
   WHERE children.userID = users.userID
   ORDER BY children.childBirthDate DESC)t1
GROUP BY child_uid

把事情放慢了.我尝试在选择查询中执行JOIN而不是选择查询,如下所示：

FROM users LEFT JOIN children ON children.userID = users.userID

但是后来我失去了“ORDER BY childBirthDate DESC”来获得这个用户最小的孩子,我失去了“GROUP BY child_uid”只让他的一个孩子

任何想法如何使事情更快但仍然有效？

P.S
抱歉我缺少英语.

编辑：

这是EXPLAIN SQL的输出

+----+--------------------+---------------+-------+----------------+---------+---------+------------------------------+-------+-----------------------------------------------------+
| id |    select_type     |     table     | type  | possible_keys  |   key   | key_len |             ref              | rows  |                        Extra                        |
+----+--------------------+---------------+-------+----------------+---------+---------+------------------------------+-------+-----------------------------------------------------+
|  1 | PRIMARY            | NULL          | NULL  | NULL           | NULL    | NULL    | NULL                         | NULL  | Impossible WHERE noticed after reading const tables |
|  4 | DEPENDENT SUBQUERY | cuponRequests | ref   | userID,cuponID | userID  | 5       | const                        | 1     | Using where                                         |
|  2 | DERIVED            | <derived3>    | ALL   | NULL           | NULL    | NULL    | NULL                         | 73526 | Using temporary; Using filesort                     |
|  3 | DERIVED            | users         | index | PRIMARY        | PRIMARY | 4       | NULL                         | 69271 | Using index; Using temporary; Using filesort        |
|  3 | DERIVED            | children      | ref   | userID         | userID  | 4       | users.userID                 | 1     |                                                     |
+----+--------------------+---------------+-------+----------------+---------+---------+------------------------------+-------+-----------------------------------------------------+

SELECT *
FROM
  (SELECT children.childrenID,users
   WHERE children.userID = users.userID
   AND children.childBirthDate <= DATE_SUB(CURDATE(),INTERVAL 5 MONTH)
   AND children.childBirthDate > DATE_SUB(CURDATE(),INTERVAL 6 MONTH)
   ORDER BY children.childBirthDate DESC)t1
GROUP BY child_uid

SELECT users.userID,children.childrenID
FROM
  (SELECT MIN(childBirthDate) AS childBirthDate,userID
      FROM children
      WHERE childBirthDate <= DATE_SUB(CURDATE(),INTERVAL 5 MONTH)
      AND childBirthDate > DATE_SUB(CURDATE(),INTERVAL 6 MONTH)
      GROUP BY userID) AS ch1
  INNER JOIN users ON users.userID = ch1.userID
  INNER JOIN children ON users.userID = children.userID AND ch1.childBirthDate = children.childBirthDate
  LEFT JOIN CuponRequests ON CuponRequests.userID = userID AND cuponID = 1
  WHERE ('Group1' LIKE users.categoryGroup OR 'Group2' LIKE users.categoryGroup)
  AND CuponRequest.ID IS NULL
  AND userID = 1
ORDER BY children.childBirthDate DESC