增强当前的SQLite查询

Question

我继承了一个旧的SQLite数据库我不应该改变（这是一个要求）。有很多表，但我会关注其中两个：

songs
----------
song_id (primary autoincrement)
group_id (external)
title
audio_file_path
wasPurchased (boolean, 0/1)

groups
----------
group_id (primary autoincrement, related to songs group_id)
group_name

目前，应用程序需要执行此查询：

SELECT song_id,title,audio_file_path,wasPurchased,G.group_name AS groupName,
G.group_id AS groupId FROM songs AS S JOIN groups AS G ON S.group_id=G.group_id 
ORDER BY groupName DESC

有没有办法，使用相同的查询，提取有多少不同的G.group_id已被购买= 0？

感谢任何帮助。

Answer 1

SELECT song_id,title,audio_file_path,wasPurchased,
G.group_name AS groupName, G.group_id AS groupId,
 SUM (SELECT DISTINCT g.group_id 
      FROM yourtables/JOIN 
      WHERE wasPurchased = 0) as nb 
FROM songs AS S 
JOIN groups AS G ON S.group_id=G.group_id 
ORDER BY groupName DESC

不确定这是否是最好的方法（从未尝试过总和中的选择但是......），但我认为它会对你有帮助。