SQL return row as empty when Select for null value or row does not exist

Question

I have table MyNumbers with data for every number like below:

Number    ServiceName   ParameterName   Value 
10431     TypeA         KeyCode1        14318
10431     TypeA         KeyCode2        3213X
10431     TypeB         KeyCode3        BlahBlah

For another Number:

Number    ServiceName   ParameterName   Value 
28659     TypeA         KeyCode2        6712X
28659     TypeB         KeyCode3        NewBlah

I need to Select for All Numbers at table and display their Value, even if the value is null or the row does not exist (like for Number 28659 above for which there is no row with ParameterName=KeyCode2. Note that for another dfferent than the above Number, the ServiceName=TypeB might be missing, etc...

The Select I am using is:

select mn1.Number, mn1.Value, mn2.Value, mn3.Value
from MyNumbers mn1, MyNumbers mn2, MyNumbers mn3
where mn2.Number = mn1.Number 
and mn3.Number = mn1.Number 
and mn1.ServiceName = 'TypeA' 
and mn1.ParameterName = 'KeyCode1' 
and mn2.ServiceName =  'TypeA' 
and mn2.ParameterName = 'KeyCode2' 
and mn3.ServiceName =  'TypeB' 
and mn3.ParameterName = 'KeyCode3';

So, for Number=28659 this returns no rows at all, because there is no row with TypeA and KeyCode1. For such cases, I want to get the populated rows (for TypeA, KeyCode2 and TypeB, KeyCode3, at example above) and empty value for the non-existent row. So, output like:

10431, 3213X, 14318, BlahBlah
28659, , 6712X, NewBlah

The last line is never displayed, this is the problem, I want all existing data to display and for non-existent row to display empty string, like above.

Thank you.

Answer 1

With your approach, you can use LEFT JOIN :

select mn1.Number, mn1.Value, mn2.Value, mn3.Value
from MyNumbers mn1 left join
     MyNumbers mn2
     on mn2.Number = mn1.Number and
        mn2.ServiceName = 'TypeA' and
        mn2.ParameterName = 'KeyCode2'left join
     MyNumbers mn3
     on mn3.Number = mn1.Number and
        mn3.ServiceName =  'TypeB' and
        mn3.ParameterName = 'KeyCode3'
where mn1.ServiceName = 'TypeA' and
      mn1.ParameterName = 'KeyCode1';

Actually, this requires something in the first column. If you have a numbers table, then:

select mn1.Number, mn1.Value, mn2.Value, mn3.Value
from Numbers n left join
     MyNumbers mn1
     on n.Number = mn1.Number and
        mn1.ServiceName = 'TypeA' and
        mn1.ParameterName = 'KeyCode1' left join
     MyNumbers mn2
     on mn2.Number = n.Number and
        mn2.ServiceName = 'TypeA' and
        mn2.ParameterName = 'KeyCode2' left join
     MyNumbers mn3
     on mn3.Number = n.Number and
        mn3.ServiceName =  'TypeB' and
        mn3.ParameterName = 'KeyCode3';

You might want to add where mn1.Number is not null or mn2.Number is not null or mn3.Number is not null if you want at least one column to have data.

Also, the Numbers table could be replaced with (select distinct Number from MyNumbers) .