在哪里IS NOT NULL

Question

如何运行MySQL查询,选择非空的所有内容？它会是这样的

SELECT * FROM schedule WHERE ((all)) IS NOT NULL

我只是删除所有并去...？

SELECT * FROM schedule WHERE IS NOT NULL

Answer 1

您必须在每列上明确说明条件,例如

SELECT *
FROM schedule 
WHERE id IS NOT NULL
  AND foo IS NOT NULL
  AND bar IS NOT NULL; -- and so on..

Answer 2

您可以连接字段以便只写入where-condition:

SELECT *
  FROM SCHEDULE
 WHERE ID || FOO || BAR IS NOT NULL;

Answer 3

它取决于你所说的"非空的一切":

• 所有列都不能 null

  select * from schedule where col1 is not null AND col2 is not null AND ..

• 至少应该有一列 non-null

  select * from schedule where col1 is not null OR col 2 is not null OR ..

至少这是你在"通用sql"中的方法.我不知道MySql是否有特殊的语法.

Answer 4

您需要通过查看information_schema数据库获取表的列的列表.

假设您的数据库已被调用,mydata并且您的表名称已被命名mytable.您可以通过发出以下语句来获取表的可空列的列表:

SELECT `COLUMN_NAME`
FROM `information_schema`.`COLUMNS`
WHERE `TABLE_SCHEMA` = 'mydata'
    AND `TABLE_NAME` = 'mytable'
    AND `IS_NULLABLE` = 'YES'

我们的最终查询将如下所示:

SELECT * FROM `mydata`.`mytable`
WHERE CONCAT(<list of columns>) IS NOT NULL

我们现在缺少的是可空列的列表,以逗号分隔.我们将使用该GROUP_CONCAT函数生成最终语句,我们将按如下方式执行:

SET @query = CONCAT(
    'SELECT * FROM `mydata`.`mytable` WHERE CONCAT(',
    (SELECT GROUP_CONCAT(COLUMN_NAME)
        FROM `information_schema`.`COLUMNS`
        WHERE `TABLE_SCHEMA` = 'mydata' AND
        `TABLE_NAME` = 'mytable'
        AND `IS_NULLABLE` = 'YES'),
    ') IS NOT NULL');

PREPARE stmt_name FROM @query;

EXECUTE stmt_name;

参考文献:

http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

http://dev.mysql.com/tech-resources/articles/4.1/prepared-statements.html