MySQL LIMIT使用SELECT COUNT（*）作為SELECT中的值

Question

嘗試做這樣的事情：

SELECT * FROM events WHERE
start_time >= DATE_SUB(NOW(),INTERVAL 6 HOUR)
LIMIT
(
SELECT COUNT(*) FROM events WHERE
start_time >= DATE_SUB(NOW(),INTERVAL 6 HOUR)
AND
start_time < NOW()
)+100
ORDER BY start_time ASC;

雖然不適合我。

Answer 1

我認為您正在嘗試執行以下操作：

SELECT e.*
FROM events e
WHERE e.start_time >= DATE_SUB(NOW(), INTERVAL 6 HOUR) AND
      e.start_time < NOW()
UNION ALL
(SELECT e.*
 FROM events e
 WHERE e.start_time >= NOW()
 ORDER BY e.start_time
 LIMIT 100
)
ORDER BY start_time;

您不能將子查詢用作limit參數。

Answer 2

像您一樣，不可能將查詢用作LIMIT函數的變量。 我會建議這樣的查詢：

SELECT *
FROM events
WHERE (
  start_time >= DATE_SUB(NOW(),INTERVAL 6 HOUR) AND
  start_time < NOW()
)
UNION ALL (
  SELECT *
  FROM events
  WHERE start_time >= NOW()
  ORDER BY start_time
  LIMIT 100
)
ORDER BY start_time ASC;

這是一個有效的sqlfiddle。

Answer 3

您可以設置一個極限變量並使用它。

SET @limit= (
    SELECT COUNT(*) FROM events WHERE
        start_time >= DATE_SUB(NOW(),INTERVAL 6 HOUR)
    AND
        start_time < NOW()
   )+100;

SELECT * FROM events WHERE
    start_time >= DATE_SUB(NOW(),INTERVAL 6 HOUR)
LIMIT @limit
ORDER BY start_time ASC;