SQLite select where empty?

Question

In SQLite, how can I select records where some_column is empty?
Empty counts as both NULL and "".

Solution 1

There are several ways, like:

where some_column is null or some_column = ''

or

where ifnull(some_column, '') = ''

or

where coalesce(some_column, '') = ''

of

where ifnull(length(some_column), 0) = 0

Solution 2

It looks like you can simply do:

SELECT * FROM your_table WHERE some_column IS NULL OR some_column = '';

Test case:

CREATE TABLE your_table (id int, some_column varchar(10));

INSERT INTO your_table VALUES (1, NULL);
INSERT INTO your_table VALUES (2, '');
INSERT INTO your_table VALUES (3, 'test');
INSERT INTO your_table VALUES (4, 'another test');
INSERT INTO your_table VALUES (5, NULL);

Result:

SELECT id FROM your_table WHERE some_column IS NULL OR some_column = '';

id        
----------
1         
2         
5    

Solution 3

Maybe you mean

select x
from some_table
where some_column is null or some_column = ''

but I can't tell since you didn't really ask a question.

Comments

[Pacerier]

What are the advantages of each solution?

[Guffa]

@Pacerier: There may be some difference in performance, but other than that it's just a matter of style.

[Pacerier]

@Guffa I mean of course the performance.. This is database isn't it? optimization is important in dbs. a little performance gain is alot

[peterchen]

length(some_column) should be avoided, since this may calculate the length on the fly - AFAIK current SQLite does for columns with text affinity. Other than that, you are at the mercy of the optimizer - though I would expect them to be identical. You could verify that by using EXPLAIN.

[Guffa]

@peterchen: Yes, it depends on what the optimiser does. I included the length example because it might actually be faster in some situation, as comparing numbers is simpler than comparing strings. If the performance for that is a concern, you should of course check what it does.