[英]Get only last messages from database mysql
我有一張像下一張一樣的桌子:
|--------|-----------|-------------|-------------|----------------|
| id | userToId | userFromId | message | date |
|--------|-----------|-------------|-------------|----------------|
| 1 | 1 | 2 | Hi |06/30/2018/18:00|
|--------|-----------|-------------|-------------|----------------|
| 2 | 1 | 2 | how r u |06/30/2018/18:01|
|--------|-----------|-------------|-------------|----------------|
| 3 | 3 | 5 | Hi |06/30/2018/17:00|
|--------|-----------|-------------|-------------|----------------|
| 4 | 1 | 5 | Hi |06/30/2018/19:00|
|--------|-----------|-------------|-------------|----------------|
| 5 | 7 | 1 | Hi |06/30/2018/19:00|
|--------|-----------|-------------|-------------|----------------|
而且,我只想獲取與提供其user ID
的特定用戶相關的最后一條消息(發送或接收)。 因此,例如,如果user ID
為1
則輸出應如下所示:
|--------|-----------|-------------|-------------|----------------|
| id | userToId | userFromId | message | date |
|--------|-----------|-------------|-------------|----------------|
| 2 | 1 | 2 | how r u |06/30/2018/18:01|
|--------|-----------|-------------|-------------|----------------|
| 4 | 1 | 5 | Hi |06/30/2018/19:00|
|--------|-----------|-------------|-------------|----------------|
| 5 | 7 | 1 | Hi |06/30/2018/19:00|
|--------|-----------|-------------|-------------|----------------|
此輸出意味着(對於id = 1
用戶)從其他用戶收到的最新消息是:
"how r u" -> from user with id = 2
"Hi" -> from user with id = 5
發送給其他用戶的最新消息是:
"Hi" -> to user with id = 7
https://www.db-fiddle.com/f/wLEHJ1EgNT9zjecYZEnCcb/0
SELECT t.*
FROM my_table t
LEFT JOIN my_table temp
ON t.userToId = temp.userToId
AND t.userFromId = temp.userFromId
AND t.date < temp.date
WHERE (t.userToId = 1
OR t.userFromId = 1)
AND temp.id IS NULL
首先,我建議在數據庫上使用規范化的日期格式(讀取Date Types )並在查詢中轉換它,如果你想以另一種格式顯示。 現在,對於您在表上使用的特定情況和datetime
格式,我將使用下一個查詢:
SELECT
m.*
FROM
msgs AS m
INNER JOIN
( SELECT
userToId,
userFromId,
MAX(STR_TO_DATE(`date`, '%m/%d/%Y/%H:%i')) AS maxDate
FROM
msgs
GROUP BY
userToId, userFromId
) AS l ON l.userToId = m.userToId
AND l.userFromId = m.userFromId
AND l.maxDate = STR_TO_DATE(m.`date`, '%m/%d/%Y/%H:%i')
WHERE
m.userToId = <your_user_id> OR m.userFromId = <your_user_id>;
您可以在此處使用一些數據查看在線示例:
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