[英]Using COUNT with a HAVING Clause in MySQL
我们很难弄清楚为什么在语句末尾使用HAVING子句时无法计数。
该语句返回结果:
SELECT lid, cid, title, url, description, date, hits, downloadratingsummary, totalvotes, totalcomments, filesize, version, homepage, ns_compat, ns_des_img, ( (2.0 * (MATCH(title) AGAINST ('fsx concorde' IN BOOLEAN MODE))) + (1.0 * (MATCH(description) AGAINST ('fsx concorde' IN BOOLEAN MODE))) + (0.5 * (MATCH(url) AGAINST ('fsx concorde' IN BOOLEAN MODE))) ) AS relevance FROM nuke_downloads_downloads WHERE ( MATCH(title,description,url) AGAINST ('fsx concorde' IN BOOLEAN MODE) ) HAVING relevance > 3.0 ORDER BY relevance DESC
该语句不返回任何内容
SELECT COUNT(*) as num, lid, cid, title, url, description, date, hits, downloadratingsummary, totalvotes, totalcomments, filesize, version, homepage, ns_compat, ns_des_img, ( (2.0 * (MATCH(title) AGAINST ('fsx concorde' IN BOOLEAN MODE))) + (1.0 * (MATCH(description) AGAINST ('fsx concorde' IN BOOLEAN MODE))) + (0.5 * (MATCH(url) AGAINST ('fsx concorde' IN BOOLEAN MODE))) ) AS relevance FROM nuke_downloads_downloads WHERE ( MATCH(title,description,url) AGAINST ('fsx concorde' IN BOOLEAN MODE) ) HAVING relevance > 3.0 ORDER BY relevance DESC
我们在这里缺少任何东西吗?
非常感谢您的帮助,并在此先感谢您。
如果只希望第一个查询返回的行数,则可以将查询封装到派生表中。
您可以跳过除了所有列relevance
从SELECT
列表和ORDER BY
:
SELECT COUNT(*)
FROM
( SELECT ( (2.0 * (MATCH ... ) AS relevance
FROM ... -- unchanged
WHERE ... -- unchanged
HAVING relevance > 3.0
-- ORDER BY removed
) AS t ;
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