Question

I want to make a table like following

| ID | Sibling1 |   Sibling2 |   Sibling 3  | Total_Siblings |
______________________________________________________________
| 1  |  Tom     |    Lisa    |    Null      |       2        | 
______________________________________________________________
| 2  |  Bart    |    Jason   |    Nelson    |       3        |
______________________________________________________________
| 3  |  George  |    Null    |    Null      |       1        |
______________________________________________________________
| 4  |  Null    |    Null    |    Null      |       0        |

For Sibling1, Sibling2, Sibling3: they are all nvarchar(50) (can’t change this as the requirement).

My concern is that how can I calculate the value for Total_Siblings so it will display the number of siblings like above, using SQL? i attempted to use (Sibling1 + Sibling 2) but it does not display the result I want.

Cheers

Answer 1

A query like this would do the trick.

SELECT ID,Sibling1,Sibling2,Sibling3
,COUNT(Sibling1)+Count(Sibling2)+Count(Sibling3) AS Total
FROM MyTable
GROUP BY ID

A little explanation is probably required here. Count with a field name will count the number of non-null values. Since you are grouping by ID, It will only ever return 0 or 1. Now, if you’re using anything other than MySQL, you’ll have to substitute

GROUP BY ID

FOR

GROUP BY ID,Sibling1,Sibling2,Sibling3

Because most other databases require that you specify all columns that don’t contain an aggregate function in the GROUP BY section.

Also, as an aside, you may want to consider changing your database schema to store the siblings in another table, so that each person can have any number of siblings.