Compatible SQL to test for not null and not empty strings

Question

I want to have compatible SQL for both Oracle database and Microsoft SQL server.

I want a compatible SQL expression that will return true for not null and not empty strings.

If I use:

column <> ''

it will work on Microsoft SQL server but not on Oracle database (as '' is null for Oracle)

If I use:

len(column) > 0

it will work on Microsoft SQL server but not on Oracle database (since it uses length() )

Answer 1

NULLIF is available on both Oracle (doc) and SQL Server (doc). This expression should work:

NULLIF(column, '') IS NOT NULL

In both servers, if column is NULL, then the output of NULLIF will just pass the NULL value through. On SQL Server, '' = '', so the output of NULLIF will be NULL. On Oracle, '' is already NULL, so it gets passed through.

This is my test on SQL Server 2008 R2 Express:

WITH SampleData AS
    (SELECT 1 AS col1, CAST(NULL AS varchar(10)) AS col2
     UNION ALL
     SELECT 2, ''
     UNION ALL
     SELECT 3, 'hello')
SELECT *
  FROM SampleData
 WHERE NULLIF(col2, '') IS NOT NULL;

And this is my test case on Oracle 10g XE:

WITH SampleData AS
    (SELECT 1 AS col1, NULL AS col2 FROM DUAL
     UNION ALL
     SELECT 2, '' FROM DUAL
     UNION ALL
     SELECT 3, 'hello' FROM DUAL)
SELECT *
  FROM SampleData
 WHERE NULLIF(col2, '') IS NOT NULL;

Both return 3 as expected.