PQgetisnull : Not not return true even value is empty in DB

I am working on bug in my Database library which use LibPQ internally.I see following behavior which looks strange to me :

For postgreSql Datatype DATE it returns true if its empty in DB For postgreSql Datatype TIME it return true if i开发者_如何学编程ts empty in DB

But for VARCHAR,SMALLINT..it return false even they were empty in DB.

PS. I have not check for other data types yet

The empty string and zero (0) are NOT the same thing as NULL. Run a form of this query to see how many NULLs vs empty strings exist for your field:

SELECT COALESCE(<field_name>,'NULL'), COUNT(*)
FROM <table_name>
WHERE <field_name> = ''
   OR <field_name> IS NULL
GROUP BY 1

Replace the empty string ('') in this query with zero to check against numeric fields.