sql select with argument which can be NULL - sql

Question

What is the best way to have a select query which has an argument which can be NULL depending on some variable in the program?
I can think of two solutions (pseudocode):
bool valueIsNull;
int value;
query = "SELECT * FROM table WHERE field ";
if (valueIsNull)
{
query += "IS NULL";
}
else
{
query += "= ?";
}
statement st = sql.prepare(query);
if (!valueIsNull)
{
st.bind(0, value);
}
or
bool valueIsNull;
int value;
query = "SELECT * FROM table WHERE field = ? OR (? IS NULL AND field IS NULL)";
statement st = sql.prepare(query);
if (valueIsNull)
{
st.bindNull(0);
st.bindNull(1);
}
else
{
st.bind(0, value);
st.bind(1, value);
}
It is a lot of code for just a simple SELECT statement and I find it just ugly and unclear.
The cleanest way would be something like:
bool valueIsNull;
int value;
query = "SELECT * FROM table WHERE field = ?"; // <-- this does not work
statement st = sql.prepare(query);
st.bind(0, value, valueIsNull); // <-- this works
Obviously this does not work. But is there a clean way to handle this?
I do not think it matter much but I am using C++, cppdb and postgresql.

Answer 1

With Postgresql (but I believe not standard) you can use
SELECT * from some_table where field IS NOT DISTINCT FROM ?;
IS NOT DISTINCT FROM, unlike plain =, is true when both sides are NULL.

Answer 2

As you've noted, the main problem with this:
SELECT * FROM table WHERE field = ? OR (? IS NULL AND field IS NULL)
is that it is actually two parameters which need to be bound.
You can get around that with a (should be fairly portable) construct like:
SELECT *
FROM table
INNER JOIN (SELECT ? AS param1 /* FROM DUAL */) AS params
ON 1 = 1
WHERE field = param1
OR COALESCE(param1, field) IS NULL