例如我创建了3个索引:
click_date-transaction表、daily_metric表order_date-交易表
我想检查我的查询是否使用索引，我使用 EXPLAIN 函数并得到此结果:
+----+--------------+--------------+-------+---------------+------------+---------+------+--------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------+--------------+-------+---------------+------------+---------+------+--------+----------------------------------------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 668 | Using temporary; Using filesort |
| 2 | DERIVED | <derived3> | ALL | NULL | NULL | NULL | NULL | 645 | |
| 2 | DERIVED | <derived4> | ALL | NULL | NULL | NULL | NULL | 495 | |
| 4 | DERIVED | transaction | ALL | order_date | NULL | NULL | NULL | 291257 | Using where; Using temporary; Using filesort |
| 3 | DERIVED | daily_metric | range | click_date | click_date | 3 | NULL | 812188 | Using where; Using temporary; Using filesort |
| 5 | UNION | <derived7> | ALL | NULL | NULL | NULL | NULL | 495 | |
| 5 | UNION | <derived6> | ALL | NULL | NULL | NULL | NULL | 645 | Using where; Not exists |
| 7 | DERIVED | transaction | ALL | order_date | NULL | NULL | NULL | 291257 | Using where; Using temporary; Using filesort |
| 6 | DERIVED | daily_metric | range | click_date | click_date | 3 | NULL | 812188 | Using where; Using temporary; Using filesort |
| NULL | UNION RESULT | <union2,5> | ALL | NULL | NULL | NULL | NULL | NULL | |
+----+--------------+--------------+-------+---------------+------------+---------+------+--------+----------------------------------------------+
在EXPLAIN结果中我看到，交易表的索引order_date没有被使用，我的理解正确吗？
daily_metric 表的索引 click_date 使用正确吗？
请告诉我如何从EXPLAIN结果中理解我创建的索引是否在查询中正确使用？
我的查询:
SELECT
partner_id,
the_date,
SUM(clicks) as clicks,
SUM(total_count) as total_count,
SUM(count) as count,
SUM(total_sum) as total_sum,
SUM(received_sum) as received_sum,
SUM(partner_fee) as partner_fee
FROM (
SELECT
clicks.partner_id,
clicks.click_date as the_date,
clicks,
orders.total_count,
orders.count,
orders.total_sum,
orders.received_sum,
orders.partner_fee
FROM
(SELECT
partner_id, click_date, sum(clicks) as clicks
FROM
daily_metric WHERE DATE(click_date) BETWEEN '2013-04-01' AND '2013-04-30'
GROUP BY partner_id , click_date) as clicks
LEFT JOIN
(SELECT
partner_id,
DATE(order_date) as order_dates,
SUM(order_sum) as total_sum,
SUM(customer_paid_sum) as received_sum,
SUM(partner_fee) as partner_fee,
count(*) as total_count,
count(CASE
WHEN status = 1 THEN 1
ELSE NULL
END) as count
FROM
transaction WHERE DATE(order_date) BETWEEN '2013-04-01' AND '2013-04-30'
GROUP BY DATE(order_date) , partner_id) as orders ON orders.partner_id = clicks.partner_id AND clicks.click_date = orders.order_dates
UNION ALL SELECT
orders.partner_id,
orders.order_dates as the_date,
clicks,
orders.total_count,
orders.count,
orders.total_sum,
orders.received_sum,
orders.partner_fee
FROM
(SELECT
partner_id, click_date, sum(clicks) as clicks
FROM
daily_metric WHERE DATE(click_date) BETWEEN '2013-04-01' AND '2013-04-30'
GROUP BY partner_id , click_date) as clicks
RIGHT JOIN
(SELECT
partner_id,
DATE(order_date) as order_dates,
SUM(order_sum) as total_sum,
SUM(customer_paid_sum) as received_sum,
SUM(partner_fee) as partner_fee,
count(*) as total_count,
count(CASE
WHEN status = 1 THEN 1
ELSE NULL
END) as count
FROM
transaction WHERE DATE(order_date) BETWEEN '2013-04-01' AND '2013-04-30'
GROUP BY DATE(order_date) , partner_id) as orders ON orders.partner_id = clicks.partner_id AND clicks.click_date = orders.order_dates
WHERE
clicks.partner_id is NULL
ORDER BY the_date DESC
) as t
GROUP BY the_date ORDER BY the_date DESC LIMIT 50 OFFSET 0
最佳答案
虽然我无法解释 EXPLAIN 转储了什么，但我认为一定有一个更简单的解决方案来解决您所拥有的问题，并提出了以下解决方案。我建议使用以下索引来优化 WHERE 日期范围和按合作伙伴分组的现有查询。
此外，当您的查询在字段上使用 FUNCTION 时，它不会利用索引。例如您的 DATE(order_date) 和 DATE(click_date)。为了更好地使用索引，请限定完整的日期/时间，例如上午 12:00(上午)到晚上 11:59。我通常会通过
x >= someDate @12:00 and x < firstDayAfterRange.
在您的示例中是(请注意，小于 5 月 1 日，截至 4 月 30 日晚上 11:59:59)
click_date >= '2013-04-01' AND click_date < '2013-05-01'
Table Index
transaction (order_date, partner_id)
daily_metric (click_date, partner_id)
现在，进行调整。由于您的点击表可能包含交易没有的条目，反之亦然，我会调整此查询以对所有可能的日期/合作伙伴进行预查询，然后左连接到相应的聚合查询，例如:
SELECT
AllParnters.Partner_ID,
AllParnters.the_Date,
coalesce( clicks.clicks, 0 ) Clicks,
coalesce( orders.total_count, 0 ) TotalCount,
coalesce( orders.count, 0 ) OrderCount,
coalesce( orders.total_sum, 0 ) OrderSum,
coalesce( orders.received_sum, 0 ) ReceivedSum,
coalesce( orders.partner_fee 0 ) PartnerFee
from
( select distinct
dm.partner_id,
DATE( dm.click_date ) as the_Date
FROM
daily_metric dm
WHERE
dm.click_date >= '2013-04-01' AND dm.click_date < '2013-05-01'
UNION
select
t.partner_id,
DATE(t.order_date) as the_Date
FROM
transaction t
WHERE
t.order_date >= '2013-04-01' AND t.order_date < '2013-05-01' ) AllParnters
LEFT JOIN
( SELECT
dm.partner_id,
DATE( dm.click_date ) sumDate,
sum( dm.clicks) as clicks
FROM
daily_metric dm
WHERE
dm.click_date >= '2013-04-01' AND dm.click_date < '2013-05-01'
GROUP BY
dm.partner_id,
DATE( dm.click_date ) ) as clicks
ON AllPartners.partner_id = clicks.partner_id
AND AllPartners.the_date = clicks.sumDate
LEFT JOIN
( SELECT
t.partner_id,
DATE(t.order_date) as sumDate,
SUM(t.order_sum) as total_sum,
SUM(t.customer_paid_sum) as received_sum,
SUM(t.partner_fee) as partner_fee,
count(*) as total_count,
count(CASE WHEN t.status = 1 THEN 1 ELSE NULL END) as COUNT
FROM
transaction t
WHERE
t.order_date >= '2013-04-01' AND t.order_date < '2013-05-01'
GROUP BY
t.partner_id,
DATE(t.order_date) ) as orders
ON AllPartners.partner_id = orders.partner_id
AND AllPartners.the_date = orders.sumDate
order by
AllPartners.the_date DESC
limit 50 offset 0
这样，第一个查询将很快在索引上从任一表中获取所有可能的组合。然后左连接最多将连接到每组一行。如果找到，则获取数字，如果没有，我将应用 COALESCE()，因此如果为 null，则默认为零。
澄清。
就像您在构建“点击”和“订单”的预聚合查询时一样，“AllPartners”是您感兴趣的日期范围内选择的不同合作伙伴和日期的 ALIAS 结果。结果列为与您的下一个查询相对应的“partner_id”和“the_date”在哪里。所以这是加入“点击”和“订单”聚合的基础。因此，由于我在别名“AllParnters”中拥有这两列，因此我只是将它们获取到字段列表，因为它们是左连接到其他别名的，并且可能不存在于相应的其他别名中。
关于MySQL显示查询中使用的索引，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25767826/