[MySQL]group by 與 if 的統計技巧

group by查詢旨在把某字段中相同的記錄合並成一列，查詢結果可受count(),sum()等統計函數影響

如下表

id	totalclick	validclick
1	3	1
2	3	1
3	5	2
4	2	1
5	3	1
6	5	2

以validclick為分組，統計每個分組的記錄數，和每個分組的totalclick總和

SELECT count(`id`),sum(`totalclick`), validclick FROM diary_log GROUP BY validclick;

結果：

count(`id`)	sum(`totalclick`)	validclick
4	11	1
2	10	2

 

配合if，可以模擬count()統計每個分組的記錄數

SELECT count(`id`), sum(if(validclick = 1,1,0)) validclick_1,sum(if(validclick = 2,1,0)) validclick_2,validclick FROM diary_log  GROUP BY validclick;

結果：

count(`id`)	validclick_1	validclick_2	validclick
4	4	0	1
2	0	2	2