如何动态地将NULL插入postgres表？

Question

I have a table like this

CREATE TABLE test(a int, b int);

The values to the table are inserted from dynamic input

$a, $b (PHP variables)

$query = "UPDATE test set a=$a where b = $b";
pg_query($db, $query);

This doesn't work when $a is empty (i.e when the user doesn't enter any value for a form field from the table). How to I get around this?

Answer 1

If $a is empty, $query will look like:

UPDATE test SET a= where b = whatever

You need to explicitly add NULL to the query string:

UPDATE test SET a=NULL where b = whatever