Mysql 计算包含特定字符串和聚合的行数

我的数据库中有以下一组行：

 USER   |  ACTIVITY
'User1' | 'User1 liked FeatureX'
'User1' | 'User1 liked FeatureY'
'User2' | 'User2 followed FeatureX'

我想运行执行以下操作的查询：

select User, 
       count(Activity like '%liked%') as LikedActivity, 
       count(Activity like '%followed%') as FollowedActivity
from db.Table 
group by USER

---

换句话说：我想为每个用户检索“功能喜欢”和“功能跟随”的数量。

在这里使用

SUM

和

CASE

表达式：

SELECT
    User, 
    SUM(CASE WHEN Activity LIKE '%liked%'    THEN 1 ELSE 0 END) AS LikedActivity, 
    SUM(CASE WHEN Activity LIKE '%followed%' THEN 1 ELSE 0 END) AS FollowedActivity
FROM db.Table 
GROUP BY User;

我们也可以在这里使用

COUNT

，这将导致一个更整洁的查询：

SELECT
    User, 
    COUNT(CASE WHEN Activity LIKE '%liked%'    THEN 1 END) AS LikedActivity, 
    COUNT(CASE WHEN Activity LIKE '%followed%' THEN 1 END) AS FollowedActivity
FROM db.Table 
GROUP BY User;

---

啊，我明白了！！非常好，谢谢！两者之间有什么性能差异吗？@Gio我认为两者的性能差异很小。您可以对两个查询运行

EXPLAIN

，以查看差异。