SQLite选择哪里空？

Question

在SQLite中,如何选择some_column为空的记录？
空计为NULL和"".

Answer 1

有几种方法,比如:

where some_column is null or some_column = ''

要么

where ifnull(some_column, '') = ''

要么

where coalesce(some_column, '') = ''

的

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

Answer 2

看起来你可以简单地做:

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

测试用例:

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);

结果:

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

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