MySQL：提取唯一日期

Question

我用

创建了一个table

CREATE TABLE visits (
  user_id int,
  event_date timestamp
);

INSERT INTO visits (user_id, event_date)
VALUES
  (1, '2021-12-22 12:12:00'),
  (1, '2021-12-23 12:12:05'),
  (1, '2021-12-24 12:13:00'),
  (1, '2021-12-24 12:14:00'),
  (1, '2022-03-10 12:14:00'),
  (1, '2022-03-11 12:14:00'),
  (2, '2021-12-23 12:12:00'),
  (1, '2022-03-12 12:14:00'),
  (2, '2021-12-23 13:12:00'),
  (1, '2022-03-13 12:14:00'),
  (1, '2022-03-14 12:14:00'),
  (3, '2021-12-25 12:12:00'),
  (1, '2022-03-15 12:14:00'),
  (1, '2022-03-20 12:14:00'),
  (1, '2022-03-21 12:14:00'),
  (1, '2022-03-23 12:14:00'),
  (1, '2022-03-24 12:14:00'),
  (1, '2022-03-25 12:14:00'),
  (3, '2021-12-30 12:12:00'),
  (3, '2021-12-31 12:12:00'),
  (3, '2021-12-31 12:12:00'),
  (4, '2022-03-21 12:12:00'),
  (4, '2022-03-22 12:12:00'),
  (4, '2022-03-23 12:12:00'),
  (4, '2022-03-24 12:12:00');

然后我尝试使用

提取独特的日期

select 
  user_id,
  distinct cast(event_date as date) as event_date
from visits;

然后我得到

ERROR 1064 (42000) at line 111: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'distinct cast(event_date as date) as event_date

来自第 3 行的访问

我做错了什么？

Answer 1

您应该将关键字 distinct 放在第一个位置：

select  distinct cast(event_date as date) as event_date, user_id
from visits;

或

select  distinct user_id, cast(event_date as date) as event_date
from visits;

Here is a demo

Answer 2

您可以使用 GROUP BY。（COUNT 列是可选的）

SELECT
count(*) "number",
user_id,
DATE(event_date) "event date"
FROM visits
GROUP BY
user_id,
DATE(event_date)
ORDER BY
user_id,
DATE(event_date);

MySQL：提取唯一日期

MySQL: extract unique dates

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