EXISTS行数

Question

SELECT * FROM table1 WHERE EXISTS (SELECT * FROM table2 WHERE *condition*)

我可以检查是否有例如3行关于table2条件？ 像

这样的东西

[...]WHERE EXISTS 3 (SELECT[...]

由于

Answer 1

您可以使用exists之外的其他内容执行此操作。例如，聚合table2并计算行数：

SELECT *
FROM table1 t1 JOIN
     (SELECT t2.??
      FROM table2 t2
      WHERE conditions (no correlation conditions)
      GROUP BY t2.??
      HAVING COUNT(*) >= 3
     ) t2
     ON t1.?? = t2.??;

Answer 2

您可以简单地计算：

SELECT * FROM table1 WHERE (SELECT COUNT(*) FROM table2 WHERE *condition*) = 3;

Answer 3

根据您对Gordon的回答的问题，您希望选择其ID作为AssociatedID三次出现的记录。因此，选择出现三次的所有AssociatedID，然后选择ID为该数据集的所有记录。

select *
from mytable 
where id in (select associatedid from mytable group by associatedid having count(*) = 3);