mysql - 在一个查询中将表连接在一起

Question

圣诞快乐。任何人都可以帮我提出针对此特定场景的查询:〜我需要生成一个事件列表，显示为每项事件注册的每种性别的 child 数量。查询会是什么？谢谢。表结构如下: 有 ACTIVITY、CHILD、CHILD ACTIVITY 表。

ACTIVITY TABLE
( activity_id[Primary Key], 
  Activity)

CHILD TABLE
( child_id[Primary Key], 
  child_name, 
  child_gender, 
  child_dob)

CHILD ACTIVITY TABLE
( activity_id[Composite Primary Key], 
  child_id[Composite Primary Key]
  Activity/Day Of Week)

Answer 1

SELECT a.activity_id, a.Activity, c.child_gender, COUNT(*)
FROM ACTIVITY a
 JOIN [CHILD ACTIVITY] ca ON a.activity_id = ca.activity_id 
 JOIN CHILD c ON ca.child_id = c.child_id
GROUP BY a.activity_id, a.Activity, c.child_gender