Question

I usq sqlite3 (on Android) and try to return a default value, if a select has to handle NULL values.

Normally this works:

SELECT ifnull(NULL, 12);
12

With a variable:
SELECT ifnull(var, 21) from (select NULL as var);
21

But the moment I use a table and this table is empty, then I don’t get anything:

SELECT ifnull(_id, 1) FROM empty_table;
<nothing here>

Even returning a simple number is not possible:

SELECT 123;
123
SELECT 234 FROM empty_table;
<nothing here>

Why does that happen? How can I still get a value out of it?

Answer 1

It’s a bit different.

When using SELECT with rows, ifnull() is evaluated once per row, so you need at least one row.

You could probably try something:

SELECT IFNULL((SELECT _id FROM empty_table LIMIT 1), 1)