Question

是否可以执行仅采用NOT NULL值的select语句？

现在我正在使用它：

SELECT * FROM table

然后我必须用php循环过滤掉空值。

有办法吗？

SELECT * (that are NOT NULL) FROM table

现在当我选择*我得到val1，val2，val3，null，val4，val5，null，null等....但我只想获得结果中不为null的值。如果没有使用循环过滤，这是否可行？

Answer 1

您应该使用IS NOT NULL。（比较运算符=和<>都会在表达式的任一侧为UNKNOWN提供NULL。）

SELECT * 
FROM table 
WHERE YourColumn IS NOT NULL;

为了完整起见，我会在MySQL中提到你也可以否定null safe equality operator，但这不是标准的SQL。

SELECT *
FROM table 
WHERE NOT (YourColumn <=> NULL);

编辑以反映评论。听起来您的桌子可能不是第一种正常形式，在这种情况下，更改结构可能会使您的任务更容易。其他几种做法虽然......

SELECT val1 AS val
FROM  your_table
WHERE val1 IS NOT NULL
UNION ALL
SELECT val2 
FROM  your_table
WHERE val2 IS NOT NULL
/*And so on for all your columns*/

上述缺点是它为每列扫描一次表多次。下面可能会避免这种情况，但我还没有在MySQL中对此进行过测试。

SELECT CASE idx
         WHEN 1 THEN val1
         WHEN 2 THEN val2
       END AS val
FROM   your_table
        /*CROSS JOIN*/
       JOIN (SELECT 1 AS idx
                   UNION ALL
                   SELECT 2) t
HAVING val IS NOT NULL  /*Can reference alias in Having in MySQL*/

Answer 2

您可以过滤掉特定列中包含NULL值的行：

SELECT col1, col2, ..., coln
FROM yourtable
WHERE somecolumn IS NOT NULL

如果要过滤掉任何列中包含null的行，请尝试以下操作：

SELECT col1, col2, ..., coln
FROM yourtable
WHERE col1 IS NOT NULL
AND col2 IS NOT NULL
-- ...
AND coln IS NOT NULL

更新：根据您的评论，也许您想要这个？

SELECT * FROM
(
    SELECT col1 AS col FROM yourtable
    UNION
    SELECT col2 AS col FROM yourtable
    UNION
    -- ...
    UNION
    SELECT coln AS col FROM yourtable
) T1
WHERE col IS NOT NULL

我对Martin说，如果你需要这样做，那么你应该改变你的数据库设计。

Answer 3

Select * from your_table 
WHERE col1 and col2 and col3 and col4 and col5 IS NOT NULL;

这种方法的唯一缺点是你只能比较5列，之后结果总是假的，所以我只比较可以NULL的字段。

Answer 4

我找到了这个解决方案：

此查询为每列选择最后一个非空值。

实施例

如果你有一张桌子：

id|title|body
1 |t1   |b1
2 |NULL |b2
3 |t3   |NULL

你得到：

title|body
t3   |b2

查询

SELECT DISTINCT (

  SELECT title
  FROM test
  WHERE title IS NOT NULL 
  ORDER BY id DESC 
  LIMIT 1
) title, (

  SELECT body
  FROM test
  WHERE body IS NOT NULL 
  ORDER BY id DESC 
  LIMIT 1
) body
FROM test

我希望能帮助你。

Answer 5

我在MySQL中使用\!命令从shell中删除NULL值：

\! mysql -e "SELECT * FROM table WHERE column = 123456\G" | grep -v NULL

最适合使用指定数据库/用户名/密码的.my.cnf。这样，您只需使用select和\! mysql e包围| grep -v NULL。

Answer 6

以下查询对我有用

当我将列的默认值设置为“ NULL”时

select * from table where column IS NOT NULL

当我将默认值设置为空时

select * from table where column <>''

Answer 7

是，请在您的查询中使用NOT NULL，如下所示。

SELECT * 
FROM table
WHERE col IS NOT NULL;

Answer 8

MYSQL IS NOT NULL WITH JOINS AND SELECT, INSERT INTO, DELETE & LOGICAL OPERATOR LIKE OR , NOT

Using IS NOT NULL On Join Conditions

 SELECT * FROM users 
 LEFT JOIN posts ON post.user_id = users.id 
 WHERE user_id IS NOT NULL;

 Using IS NOT NULL With AND Logical Operator

 SELECT * FROM users 
 WHERE email_address IS NOT NULL 
 AND mobile_number IS NOT NULL;

Using IS NOT NULL With OR Logical Operator

 SELECT * FROM users 
 WHERE email_address IS NOT NULL 
 OR mobile_number IS NOT NULL;

Answer 9

SELECT duration,id FROM `tickets` WHERE duration !=""

Answer 10

SELECT * FROM TABLE_NAME
where COLUMN_NAME <> '';

MySQL SELECT只是非空值

10 个答案: