在 MySQL 中获取至少 x 行数
你好，我正在尝试让 mysql 查询正常工作，但说实话，我不知道从哪里开始，我认为 count 函数可以工作，但不确定。
我想做的是进行选择，但如果计数的行数少于 5 行，则与另一个查询/where 子句联合，直到达到 5 行。
所以基本上至少要 5 行并继续连接行，直到达到 5 行或更多...
$myquery_mysql = mysql_query("(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' AND city = '".mysql_real_escape_string($GLOBALS['user_city'])."')
UNION ALL
(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' AND province = '".mysql_real_escape_string($GLOBALS['user_province'])."' )
UNION ALL
(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' )" or die(mysql_error());
我会做类似的事情吗...
$myquery_mysql = mysql_query("(SELECT title, city, ad_image, rent, uniqid count(if title > 5) THEN FROM rentals WHERE front_page_ad = '1' AND paid = '1' )"
UNION ALL
(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' AND province = '".mysql_real_escape_string($GLOBALS['user_province'])."' )
ELSE FROM rentals WHERE front_page_ad = '1' AND paid = '1' )" END ;
or die(mysql_error());
我知道这是不对的，但我只是想弄清楚。
Hi I am trying to get a mysql query to work properly but to be honest Im not sure where to start, I think count function would work but not sure.
What I am trying to do is do a select but if there are less than 5 rows counted than union with another query/where clause until 5 is reached.
So basically go at least 5 rows and keep joining rows until 5 or more is reached...
$myquery_mysql = mysql_query("(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' AND city = '".mysql_real_escape_string($GLOBALS['user_city'])."')
UNION ALL
(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' AND province = '".mysql_real_escape_string($GLOBALS['user_province'])."' )
UNION ALL
(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' )" or die(mysql_error());
Would I do something like...
$myquery_mysql = mysql_query("(SELECT title, city, ad_image, rent, uniqid count(if title > 5) THEN FROM rentals WHERE front_page_ad = '1' AND paid = '1' )"
UNION ALL
(SELECT title, city, ad_image, rent, uniqid FROM rentals WHERE front_page_ad = '1' AND paid = '1' AND province = '".mysql_real_escape_string($GLOBALS['user_province'])."' )
ELSE FROM rentals WHERE front_page_ad = '1' AND paid = '1' )" END ;
or die(mysql_error());
I know this isn't right, but I am just trying to figure it out.
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评论（2）
您可以在末尾添加一个
LIMIT 5，这样它将使用所有联合执行整个查询，然后选择前 5 个结果，只要您不给它 ORDER BY 就应该按照您进行工会的顺序列出它们。因此，如果第一个查询有 5 个结果，它将只获取这些结果，但如果没有，它将获取接下来 2 个并集的结果。只要您的工会不太耗时，这似乎就是一个不错的行动方案。
You could add a
LIMIT 5at the end, so it will do the entire query with all the unions and then select the top 5 results, as long as you're not giving it an ORDER BY it should list them in the order you do your unions.So if the first query has 5 results it'll just take those, but if not, it'll take results from the next 2 unions. As long as your unions aren't very time consuming this seems like a good course of action.
我会这样做：
desc，因此匹配值的顺序高于不匹配的值（将为null）I'd do:
descso matching values order higher than non-matching (which will benull)