PostgreSQL,从最大id中选择

Question

通过在PG 9.1上使用libpq,我试图编写查询以从具有最高索引'my_id'的行获取值:

SELECT my_id, col2, col3 
FROM mytable 
WHERE my_id = MAX(my_id)

这给了我错误:

错误:WHERE子句中不允许聚合...

如何正确编写这样的查询？

Answer 1

如果您的目标是获取具有最高my_id值的行,则以下查询应实现相同的目标.

SELECT my_id, col2, col3 
FROM mytable 
ORDER BY my_id DESC 
LIMIT 1

Answer 2

只需订购my_id并只带第一条记录limit 1

SELECT my_id, col2, col3
FROM mytable 
order by my_id desc
limit 1

另一种但性能较差的方式是

SELECT my_id, col2, col3
FROM mytable 
where my_id = (select max(my_id) from mytable)

Answer 3

子查询可以帮助您

SELECT my_id, col2, col3 FROM mytable WHERE my_id = (select MAX(my_id) FROM mytable)