SQL SQLite 选择哪里为空？
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SQLite select where empty?
提问by Timo Huovinen
In SQLite, how can I select records where some_column is empty?
Empty counts as both NULL and "".
在 SQLite 中，如何选择 some_column 为空的记录？
Empty 算作 NULL 和 ""。
回答by Guffa
There are several ways, like:
有几种方法，例如：
where some_column is null or some_column = ''
or
或者
where ifnull(some_column, '') = ''
or
或者
where coalesce(some_column, '') = ''
of
的
where ifnull(length(some_column), 0) = 0
回答by Daniel Vassallo
It looks like you can simply do:
看起来你可以简单地做：
SELECT * FROM your_table WHERE some_column IS NULL OR some_column = '';
Test case:
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);
Result:
结果：
SELECT id FROM your_table WHERE some_column IS NULL OR some_column = '';
id
----------
1
2
5
回答by μBio
Maybe you mean
也许你的意思是
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.
但我不能说，因为你并没有真正提出问题。
回答by mahesh takkalwad
You can do this with the following:
您可以使用以下方法执行此操作：
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.
这将为您提供列值为空或空白的行数。
