Php 当前行上的MYSQL计数子查询
我在这个问题上遇到了麻烦,希望有人能帮助我Php 当前行上的MYSQL计数子查询,php,mysql,sql,count,subquery,Php,Mysql,Sql,Count,Subquery,我在这个问题上遇到了麻烦,希望有人能帮助我 SELECT myTable.id, myTable.subject, myTable.upvotes, myTable.downvotes, (SELECT COUNT(id) FROM myTable WHERE myTable.thread = myTable.id) AS comments_count FROM myTable 基本上我有一个包含帖子和评论的表,评论线
SELECT
myTable.id,
myTable.subject,
myTable.upvotes,
myTable.downvotes,
(SELECT COUNT(id)
FROM myTable
WHERE myTable.thread = myTable.id) AS comments_count
FROM myTable
基本上我有一个包含帖子和评论的表,评论线程与原始帖子的id绑定。在我的查询中,我想显示当前id/行的所有行中有多少个relpie(多少线程=id)
我希望这是有意义的:)您需要在子查询中使用新别名指定要匹配的表,否则它将匹配同一个表中id为的线程
SELECT
m.id,
m.subject,
m.upvotes,
m.downvotes,
(SELECT COUNT(id)
FROM myTable
WHERE myTable.thread = m.id) AS comments_count
FROM myTable m
或者最好使用LEFT JOIN
SELECT
m.id,
m.subject,
m.upvotes,
m.downvotes,
COUNT(mm.id) AS comments_count
FROM myTable m
LEFT JOIN myTable mm ON(mm.thread = m.id)
GROUP BY m.id
啊,谢谢你!这很有道理。我应该用化名。我也会尝试左连接。再次感谢!!