MySQL .. 如果 COUNT 返回大于 0 的任何值，则返回“1”
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MySQL.. Return '1' if a COUNT returns anything greater than 0
提问by kimion09
I'm trying to create MySQL query that essentially returns true or false. I'd like to run
我正在尝试创建基本上返回 true 或 false 的 MySQL 查询。我想跑
SELECT COUNT(id)
FROM comments
WHERE comment_date >= 1306904400
AND user_id = 1
So if the user posted in the forum 10 times this month, I'd like it to return just 1, otherwise I'd like it to return 0 to indicate they haven't.
因此，如果用户本月在论坛上发帖 10 次，我希望它只返回 1，否则我希望它返回 0 以表明他们没有。
Is that possible efficiently within SQL?
这在 SQL 中是否可能有效？
回答by mu is too short
If you don't mind MySQL-specific things then you could use IF:
如果您不介意特定于 MySQL 的事情，那么您可以使用IF：
select if(count(id) >= 10, 1, 0)
from comments
where comment_date >= 130690440
and user_id = 1
Or MySQL booleans(which are 1 for true and 0 for false):
或MySQL 布尔值（1 表示真，0 表示假）：
select count(id) >= 10
from comments
where comment_date >= 130690440
and user_id = 1
If you want to stick to standard SQL, then CASEis your friend:
如果您想坚持使用标准 SQL，那么CASE您的朋友是：
select case when count(id) >= 10 then 1 else 0 end
from comments
where comment_date >= 130690440
and user_id = 1
回答by Xint0
Use CASE:
使用CASE：
SELECT CASE WHEN COUNT(*) > 0 THEN 1 ELSE 0 END AS `flag`
FROM `comments`
WHERE `comment_date` >= 1306904400 AND `user_id` = 1
回答by Michael Dean
You don't need to count all the matching records, just find if one exists. Unfortunately, MySQL doesn't appear to support IF EXISTSas Microsoft SQL Server does. However, you can use a subselect with LIMITto fake it:
您不需要计算所有匹配的记录，只需查找是否存在。不幸的是，MySQL 似乎不像IF EXISTSMicrosoft SQL Server 那样支持。但是，您可以使用子选择 withLIMIT来伪造它：
SELECT COUNT(1) AS has_comments FROM (SELECT id FROM comments WHERE comment_date >= 1306904400 AND user_id = 1 LIMIT 0, 1) t;
回答by Hyman
I know this is an old thread, but here's another way to accomplish this:
我知道这是一个旧线程，但这是实现此目的的另一种方法：
SELECT COUNT(id), 1 % (1 + count(id)) as greaterThanZero
FROM comments
WHERE comment_date >= 1306904400
AND user_id = 1
SELECT COUNT(id), 1 % (1 + count(id)) as greaterThanZero
FROM comments
WHERE comment_date >= 1306904400
AND user_id = 1
回答by Rucent88
I use a LIMIT to do something similar, and just evaluate it in my code. The SQL will stop after finding 10 matches.
我使用 LIMIT 来做类似的事情，并在我的代码中对其进行评估。找到 10 个匹配项后，SQL 将停止。
SELECT id FROM {mytable}
WHERE comment_date >= 1306904400
AND user_id = 1
LIMIT 10
PHP requesting a minimum of 10 posts.
PHP 要求至少 10 个帖子。
if(my_db_query() != 10)
not_enough_posts();
回答by jcomeau_ictx
perhaps:
也许：
SELECT (SELECT COUNT(id) FROM comments
WHERE comment_date >= 1306904400 AND user_id = 1) > 10
