Question

我有2张桌子，1张是Persons，1张是Relationships。

我想要找回孩子最多的人。

目前我正在加入这样的表：

SELECT 
   PERSONS.ID, 
   PERSONS.NATIVE_COUNTRY, 
   RELATIONSHIPS.PERSON_ID, 
   RELATIONSHIPS.RELATION 
FROM PERSONS
INNER JOIN RELATIONSHIPS ON RELATIONSHIPS.PERSON_ID = ID 
                            AND RELATIONSHIPS.RELATION = 'child';

现在我正在尝试计算PERSONS.ID并获得最大值，但不知道该怎么做。

Answer 1

你可以使用分区......

SELECT PERSONS.ID, PERSONS.NATIVE_COUNTRY, RELATIONSHIPS.PERSON_ID, 
       RELATIONSHIPS.RELATION,
       count(*) over (partition by Persons.ID order by Persons.ID)
FROM PERSONS
INNER JOIN RELATIONSHIPS ON RELATIONSHIPS.PERSON_ID = ID AND 
                            RELATIONSHIPS.RELATION = 'child';

另外，如果你不喜欢

分区，你可以做简单的GROUP BY

SELECT PERSONS.ID, PERSONS.NATIVE_COUNTRY, RELATIONSHIPS.PERSON_ID, 
       RELATIONSHIPS.RELATION,
       COUNT(*)
FROM PERSONS
INNER JOIN RELATIONSHIPS ON RELATIONSHIPS.PERSON_ID = ID AND 
                            RELATIONSHIPS.RELATION = 'child';
GROUP BY  PERSONS.ID, PERSONS.NATIVE_COUNTRY, RELATIONSHIPS.PERSON_ID,
          RELATIONSHIPS.RELATION

此外，使用连接时尝试使用别名，它的可读性更好，没有理由使用大写字符

Answer 2

您可以尝试使用group by：

SELECT PERSONS.ID, COUNT(*) "No of Children" FROM PERSONS INNER JOIN RELATIONSHIPS ON RELATIONSHIPS.PERSON_ID = ID AND RELATIONSHIPS.RELATION = 'child' GROUP BY persons.id;

连接表上的SQL计数

2 个答案: