Question

I have a table like the following

id | name     | pid

1  | sam      | NULL

2  | sams ref | 1

3  | pam      | NULL

For the first time the first row gets inserted which will have pid as null
I insert a row which is related to the first row
and then i insert a row which is new and which may be referred by another row in future.

now i want only the third row to be displayed and not the first and second row as the second row contains the reference of first row.

so if any row has a reference to another row then both the rows should not be displayed.

Only rows which is not having any reference should be displayed.

BESIDES, IS IT A GOOD PRACTICE? PLEASE ADVICE ON THIS.

Answer 1

use

SELECT 
A.*
FROM myTable A
LEFT OUTER JOIN MyTable B ON B.PID = A.ID
WHERE A.PID IS NULL AND B.ID IS NULL

OR

SELECT 
A.*
FROM MyTable A
WHERE A.ID NOT IN
(
SELECT X.ID FROM MyTable X WHERE X.PID IS NOT NULL
UNION
SELECT Y.PID FROM MyTable Y WHERE Y.PID IS NOT NULL
)

As to whether this is good pratcice:

without knowing the requirements etc. I don’t see how to discuss this…