SQLite select where empty?

问题:

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

回答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

回答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    

回答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.

回答4:

You can do this with the following:

int counter = 0;
String sql = "SELECT projectName,Owner " + "FROM Project WHERE Owner= ?";
PreparedStatement prep = conn.prepareStatement(sql);
prep.setString(1, "");
ResultSet rs = prep.executeQuery();
while (rs.next()) {
    counter++;
}
System.out.println(counter);

This will give you the no of rows where the column value is null or blank.