Question

Question is as follows:

There are 2 related tables (am giving some sample values for making it simplified):

Circuit
--------
id    name
1      a
2      b
3      c

Circuit_Dependent
-----------------
id    depend_id
1     2
1     3

the tables are related and second table tells the relation with the circuit id’s.
Situation is query needed for:
1) list the circuit name which has the circuit_dependency
output expected:

name   dependent_name
a      b
a      c

2) list the circuit name and count(no of dependancies)
output expected:

name   count
a      2

appreciate help.

Answer 1

First query could be:

SELECT c1.`name`, c2.`name`
FROM Circuit_Dependent cd INNER JOIN Circuit c1 
    ON cd.id = c1.id    
INNER JOIN Circuit c2 
    ON cd.depend_id = c2.id

Second query could be this one:

SELECT c.`name`, COUNT(DISTINCT cd.depend_id) AS count 
FROM circuit c INNER JOIN Circuit_Dependent cd
    ON c.id = cd.id
GROUP BY c.id