sql - How to select rows having column value as null?

Question

Consider following database table:

id      |  is_visible
________|_______________
1       |  true
2       |  false
3       |               -- i.e. null

I want to select all the rows having is_visible = null. I tried the following queries:

SELECT * FROM tab WHERE is_visible = null;     -- 0 results
SELECT * FROM tab WHERE is_visible <> true;    -- only fields with false value
SELECT * FROM tab WHERE is_visible <> false;   -- only fields with true

I tried it in postgresql and sql server
How to select rows having is_visible = null?

Answer 1

In both Postgres and SQL server,

SELECT * FROM tab WHERE is_visible is null;

If you want to select the rows for which column values are not null, then use is not null operator:

SELECT * FROM tab WHERE is_visible is not null;