Question

Table1

    CatId     Name
    1       Category1
    2       Category2
    3       Category3

Table2

FieldId     FieldName    FieldValue   Category
1            Field1        Value1        1
2            Field2        NULL          1
3            Field3        NULL          2
4            Field4        NULL          2
5            Field5        Value2        3
6            Field6        Value3        3

I have a table structure as shown above. I want to fetch fields under category when any of the Fieldvalue is not null under that category. For my above example result should be:

FieldId     FieldName    FieldValue   Category
    1         Field1        Value1        1
    2         Field2        NULL          1
    5         Field5        Value2        3
    6         Field6        Value3        3

As you can see under category1 field2 has null value but it is still displayed. Under category 2 both field3 and field4 has null values and so it should not be selected.

Can someone help me with sql query for the above problem? One way i thought is to use groupby category and see for the count(FieldValue)>0 where fieldvalue is not null. but i am stuck how to bring this logic into sql?

Thanks in advance.

Answer 1

SELECT
    FieldId 
  , FieldName 
  , FieldValue 
  , Category
FROM 
    Table2 AS t
WHERE
    EXISTS
        ( SELECT *
          FROM Table2 AS tn
          WHERE tn.Category = t.Category
            AND tn.FieldValue IS NOT NULL
        ) ;

or:

SELECT
    t.FieldId 
  , t.FieldName 
  , t.FieldValue 
  , t.Category
FROM 
        Table2 AS t
    JOIN
        ( SELECT Category
          FROM Table2
          GROUP BY Category
          HAVING MIN(FieldValue) IS NOT NULL
        ) AS tn 
      ON tn.Category = t.Category ;