How to implement a "hasChildren" SELECT statement in SQL?

Question

Let's say I have the following table:

ID | parentID | MoreStuff
1  | -1       |  ...
2  |  1       |  ...
3  |  1       |  ...
4  |  2       |  ...
5  |  1       |  ...

How can I generate an SQL SELECT statement to find out if a specific row has children? In other words, I want to know if ID 1 has children, which in this case it has 3.

I'm not sure how to create the SQL statement:

SELECT ID, hasChildren FROM myTable;

What would be replaced for hasChildren in the above SQL SELECT statement?

Answer 1

No group version:

SELECT MyTable.Id, CASE WHEN EXISTS 
    (SELECT TOP 1 1  --you can actually select anything you want here
     FROM MyTable MyTableCheck 
     WHERE MyTableCheck.ParentId = MyTable.Id
    ) THEN 1 ELSE 0 END AS HasRows
FROM MyTable