SQL Retrieve records with values on a field while also retrieving records that are null-CodePudding

I have this table of records and I want to retrieve the records that have values for one field while also retrieving the records that are null on the same field.

CodePudding user response：

From the requirements posted it seems you want to quell rows that are null in Field 3 if there is another row that is non-null in Field 3 for the same values of Field1 and Field2

SELECT Field1, Field2, MAX(Field3) 
FROM t 
GROUP BY Field1, Field2

If you'll have multiple rows that have values and you want to keep them all you could do something with a union:

SELECT Field1, Field2, Field3 
FROM t
WHERE Field3 IS NOT NULL

UNION ALL

SELECT Field1, Field2, NULL
FROM t
GROUP BY Field1, Field2
HAVING COUNT(Field3) = 0

If gets you all the non nulls, plus all rows where counting Field3 results in 0 (i.e. field3 has only null for the pair)