MySQL只計算新記錄

Question

如何編寫一個MySQL查詢來實現這個任務？

表：作家

w_id w_name 
--------------- 
    1  Michael 
    2  Samantha 
    3  John 
--------------- 

表：文章

a_id w_id timestamp a_name 
---------------------------------------- 
    1  1  1  PHP programming 
    2  3  3  Other programming languages 
    3  3  5  Another article 
    4  2  15  Web design 
    5  1  20  MySQL 
---------------------------------------- 

需要COUNT只有那些作家誰發表了他們的第一篇文章不早於。
（僅誰發表至少一篇文章可以算作作家）

在這個例子中，結果將是： （一個作家 - 薩曼莎）

SQL代碼進行測試in this SQLFiddle

Answer 1

您需要的雙重選擇。

首先，你取w_id，加上第一篇文章的時間戳：

SELECT w_id, MIN(timestamp) as publish FROM articles GROUP BY w_id 

然後你要求publish不早於5：

SELECT w_id, MIN(timestamp) as publish 
    FROM articles 
    GROUP BY w_id 
    HAVING publish >= 5; 

然後你加入這個 「表」 與writers如果你願意，可以得到這個名字。

但如果你只想計數，你不需要writers表都：

SELECT COUNT(*) AS answer FROM 
    (SELECT w_id, MIN(timestamp) AS publish 
     FROM articles 
     GROUP BY w_id 
     HAVING publish >= 5 
) AS counter; 

測試：http://sqlfiddle.com/#!2/0e90f/30/0

Answer 2

select 
    w_name 
from writers w 
join articles a on w.w_id = a.w_id 
group by w.w_id,w.w_name 
having min(timestamp)>=5 

與小提琴.. http://sqlfiddle.com/#!2/0e90f/11/0

或數..

select 
count(w_name) 
from writers w 
join articles a on w.w_id = a.w_id 
group by w.w_id,w.w_name 
having min(timestamp)>=5 

與小提琴.. http://sqlfiddle.com/#!2/0e90f/27/0

Answer 3

你需要有一個子查詢得到作家的最低timestamp。結果將被計入sinceyou不能聚集一列，它是已經彙總（例如）。 COUNT（MIN（列名）））

SELECT COUNT(*) totalWriters 
FROM 
(
    SELECT a.w_id, MIN(b.`timestamp`) 
    FROM writers a 
      INNER JOIN articles b 
      ON a.w_id = b.w_id 
    GROUP BY a.w_id 
    HAVING MIN(b.`timestamp`) >= 5 
) a 

SQLFiddle Demo

Answer 4

一個簡單的方法：

SELECT COUNT(DISTINCT w_id) 
FROM writers 
WHERE w_id NOT IN 
(SELECT w_id from articles 
WHERE timestamp <=5) 

Answer 5

select count(*) 
from (
    select w_id, min(`timestamp`) as `timestamp` 
    from articles 
    group by w_id 
) s 
where `timestamp` >= 5 

Answer 6

select count(1) from (
    select w.w_id, count(a.timestamp) cnt from writers w 
    inner join articles a on a.w_id = w.w_id 
    group by w.w_id 
) t 
inner join articles art on art.w_id = t.w_id 
where t.cnt = 1 and art.timestamp > 5 

Answer 7

試試這個，我哈剛纔已經測試..

select* from (select tblw.w_id, count(tblart.timestamp) count from writers tblw inner join articles tblart on tblart.w_id = tblw.w_id group by tblw.w_id) temp inner join articles art on art.w_id = temp .w_id where temp .count = 1 and art.timestamp > 5 

Answer 8

這很容易，這裏是查詢：

SELECT count(DISTINCT w_id) 
FROM articles 
WHERE TIMESTAMP>=5 
AND w_id NOT IN (SELECT w_id FROM articles WHERE TIMESTAMP<5); 

見SQL Fiddle