What is the best way to convert an int or null to boolean value in an SQL query?

Question

What is the best way to convert an int or null to boolean value in an SQL query, such that:

• Any non-null value is TRUE in the results
• Any

Answer 1

In Oracle, assuming you use 0 for false and 1 for true:-

SELECT DECODE( col, NULL, 0, 1) FROM ...

You can also write this using the CASE syntax, but the above is idiomatic in Oracle. DECODE is a bit like a switch/case; if col is NULL then 0 is returned, else 1.

Answer 2

The shortest one I know for Oracle:

SELECT NVL2(nullableColumn, 1, 0) FROM someTable

NVL2(value, ifNotNull, ifNull) returns ifNotNull if the value is not null, and ifNull otherwise.

Answer 3

Assuming you want 0,1 value as a return, and that we are talking about integer I would use the logic specified by Torbjörn and wrap it in the function

create function dbo.isNotNull(@a int)
returns bit
as
begin
return isnull(@a-@a+1,0)
end

so then you can use it whenever you need by simply calling

select dbo.isNotNull(myIntColumn) from myTable

The answer provided by Tomalak is more universal though as it would work with any data type

Answer 4

No need to use case... when:

select (column_name is not null) as result from table_name;

Returns 1 for all fields not NULL and 0 for all fields that are NULL, which is as close as you can get to booleans in SQL.