按第一次和最后一次出现分组 [英] group by first and last occurrence
问题描述
我有一张像下面这样的表:
I have a table like the following one:
+-------------+--------------+
| current_day | browser |
+-------------+--------------+
| 2016-05-02 | Safari |
| 2016-05-03 | Safari |
| 2016-05-04 | Safari |
| 2016-05-05 | Safari |
| 2016-05-06 | Safari |
| 2016-05-07 | Safari |
| 2016-05-08 | Safari |
| 2016-05-09 | Opera |
| 2016-05-10 | Opera |
| 2016-05-11 | Opera |
| 2016-05-12 | Opera |
| 2016-05-13 | Opera |
| 2016-05-14 | Opera |
| 2016-05-15 | Chrome |
| 2016-05-16 | Firefox |
| 2016-05-17 | Firefox |
| 2016-05-18 | Firefox |
| 2016-05-19 | Firefox |
| 2016-05-20 | Firefox |
| 2016-05-21 | Firefox |
| 2016-05-22 | Firefox |
| 2016-05-23 | Safari |
| 2016-05-24 | Safari |
| 2016-05-25 | Safari |
| 2016-05-26 | Safari |
| 2016-05-27 | Safari |
| 2016-05-28 | Safari |
| 2016-05-29 | Safari |
| 2016-05-30 | Opera |
| 2016-05-31 | Opera |
| 2016-06-01 | Opera |
| 2016-06-02 | Firefox |
| 2016-06-03 | Firefox |
| 2016-06-04 | Firefox |
| 2016-06-05 | Firefox |
| 2016-06-06 | Firefox |
| 2016-06-07 | Firefox |
| 2016-06-08 | Firefox |
| 2016-06-09 | Chrome |
| 2016-06-10 | Chrome |
| 2016-06-11 | Chrome |
| 2016-06-12 | Chrome |
| 2016-06-13 | Chrome |
| 2016-06-14 | Chrome |
| 2016-06-15 | Chrome |
| 2016-06-16 | Chrome |
+-------------+--------------+
我想提取浏览器"列中每个序列的第一次和最后一次出现,即以下结果:
I would like to extract the first and last occurrence of each sequence in the 'browser' column, in other words the following result:
+-------------+--------------+
| current_day | browser |
+-------------+--------------+
| 2016-05-02 | Safari |
| 2016-05-08 | Safari |
| 2016-05-09 | Opera |
| 2016-05-14 | Opera |
| 2016-05-15 | Chrome |
| 2016-05-16 | Firefox |
| 2016-05-22 | Firefox |
| 2016-05-23 | Safari |
| 2016-05-29 | Safari |
| 2016-05-30 | Opera |
| 2016-06-01 | Opera |
| 2016-06-02 | Firefox |
| 2016-06-08 | Firefox |
| 2016-06-09 | Chrome |
| 2016-06-16 | Chrome |
+-------------+--------------+
是否可以/方便地创建一个 MYSQL 查询?还是提取所有结果并用php进行一些后处理更好?
Is it possible/convenient to create a MYSQL query? Or is it better to extract all results and perform some post-processing with php?
推荐答案
您可以使用以下查询:
SELECT MIN(current_day) AS start_day,
MAX(current_day) AS stop_day,
browser
FROM (
SELECT current_day, browser,
@grp := IF(@br = browser, @grp,
IF(@br := browser, @grp+1, @grp+1)) AS grp
FROM mytable
CROSS JOIN (SELECT @grp := 0, @br := '') AS vars
ORDER BY current_day) AS t
GROUP BY browser, grp
上述查询使用变量,以识别具有相同browser
值的连续记录的孤岛.它为每个浏览器返回一行.如果您想为每个最小/最大日期获得 两 行,您必须重复相同的子查询两次并使用 UNION
.
The above query uses variables, in order to identify islands of consecutive records having the same browser
value. It returns a single row per browser.
You have to repeat the same subquery twice and use UNION
if you want to get two separate lines for each of the min/max dates.
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