Replacing "(null)" with blank cell in SQL query result - sql

Question

I believe what I'm asking here is possible, but I haven't find a way yet :
Some cells in the result of my SQL SELECT-FROM-WHERE query are blank, and in DbVisualizer, (null) is written inside. I'd like to display a blank cell instead.
I've already tried with CASE-WHEN and the NVL operator, but it won't let me replace it by a blank '', I'm forced to use some ' ' or 'message'.
I know I could just delete these spaces or messages with Excel later, but I'd like to know if there is a way to do it directly with DbVisualizer, instead of this workaround.
EDIT: Here is what my request looks like :
SELECT *things*,
CASE WHEN
(SELECT COUNT(*) FROM table d2 WHERE *join-condition* AND *other condition*) = 1
THEN
(*sub-select query*)
ELSE
''
END
AS NAME,
*other things*
FROM table d1
WHERE *something*
Thanks a lot !

Answer 1

Did you try standard SQL function coalesce(), as below ?
SELECT COALESCE(columnName, '') AS ColumnName FROM tableName;
Syntax:
COALESCE (expr1, expr2)
is equivalent to:
CASE WHEN expr1 IS NOT NULL THEN expr1 ELSE expr2 END
Similarly,
COALESCE (expr1, expr2, ..., exprn), for n>=3
is equivalent to:
CASE WHEN expr1 IS NOT NULL THEN expr1
ELSE COALESCE (expr2, ..., exprn) END
Above examples are from Database SQL Language Reference

Answer 2

The problem in your query is the following ELSE part of the CASE expression:
ELSE
''
In Oracle, an empty string is considered as NULL value. So, all you need to do is use something else instead of ''.
For example, to use a space instead of NULL:
ELSE
' '
Update The issue is the DbVisualizer tool. OP is on version 8.0.12. Prior to version 9.2.8 it cannot show NULL as an empty string. However, as discussed in this forum, it has been fixed in DbVisualizer 9.2.8.

Answer 3

Standard SQL provides COALESCE(expr1, expr2, ...) as suggested by #Shishir.
COALESCE() takes a variable amount of arguments and returns the first expression that is NOT NULL
MySQL also provides IFNULL(expr1,expr2), which returns expr2 when expr1 IS NULL
Examples
SELECT
COALESCE(field1, ''),
COALESCE(field1, field2, field3)
IFNULL(field1, ''),
IFNULL(field1, field2)
FROM table