有关嵌套查询主题的SQL查询

Question

查询显示所有“父亲（丈夫）”名称，按字母顺序从Guardian表中显示其“妻子”的总数（使用嵌套查询查找妻子数）。

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Answer 1

您可以使用自我加入和分组

 select a.guardianName as husband_name, count(*) as count_of_wives
 from my_table a 
 left join my_table b  on b.husband_id = a.guardianId
 where a.husband_id is null 
 group by a.guardianName