mysql - 需要对 MySQL 连接查询进行计数

Question

查看了具有相似标题的问题，没有任何问题足以让这个查询正常工作。我知道这可能相当简单。

实际查询是这样的:

select entries.id, entry_id, user_id, person_id, campaign_id, mood_id, entries.created, deleted_date, entries.modified, entry_type, walking_hash 

 from entries, users 

where users.id = entries.user_id and users.is_deleted = 0 and entries.is_deleted = 0 

and entries.entry_type in ('xyz', 'abc', 'def', 'lmno')

为了得到计数，我尝试了这个:

select count(entries.id, entry_id, user_id, person_id, campaign_id, mood_id, entries.created, deleted_date, entries.modified, entry_type, walking_hash) 

from entries, users 

where users.id = entries.user_id and users.is_deleted = 0 and entries.is_deleted = 0 and entries.entry_type in ('xyz', 'abc', 'def', 'lmno')

但这会抛出一个非描述性错误并且不会运行。

Answer 1

你到底想数什么？只是行数？使用 COUNT(*)。使用 COUNT(column) 计算该列中的所有非 NULL 值。

查询将只返回一行，即计数。

select count(*) as count
from entries, users 
where users.id = entries.user_id and users.is_deleted = 0 and entries.is_deleted = 0 
and entries.entry_type in ('xyz', 'abc', 'def', 'lmno')