如何编写MySQL查询?

您可以按应用程序分组,然后对事件使用条件计数。

SELECT
APP,
COUNT(CASE WHEN EVENT = 'clk' THEN 1 END) AS clk,
COUNT(CASE WHEN EVENT = 'imp' THEN 1 END) AS imp,
COUNT(CASE WHEN EVENT = 'req' THEN 1 END) AS req
FROM yourtable
GROUP BY APP
ORDER BY APP;

SQL小提琴示例 here

MySQL是条件聚合的简写,因此您可以执行以下操作:

select app, 
       sum(EVENT = 'clk') as clk,
       sum(EVENT = 'imp') as imp,
       sum(EVENT = 'req') as req
from table t
group by app;

这个 SQLfiddle 表明它起作用了

你可以试着用 聚合函数条件

SELECT APP,
       SUM(CASE WHEN EVENT ='clk' THEN 1 ELSE 0 END) clk,
       SUM(CASE WHEN EVENT ='imp' THEN 1 ELSE 0 END) imp,
       SUM(CASE WHEN EVENT ='req' THEN 1 ELSE 0 END) req
FROM T
GROUP BY APP