I was asked this question at an interview, but I was not familiar with SQL.
I was hoping someone could help me out on the query, so that I can understand the concept. 

```
"id"  "name"   "parentid"
------------------------
"1"   "BOSS1"  null
"2"   "A"      "1"
"3"   "B"      "1"
"4"   "C"      "3"
"5"   "BOSS2"  null
"6"   "Q"      "5"
"7"   "T"      "6"

```

1. Given an id, find all the children

so for 1, it should print 1, 2 ,3, 4

I think this is pretty easy, but I can't figure out how to construct the query using union...

thanks