MariaDB无法评估SELECT 1 WHERE NULL = NULL; [英] MariaDB cannot evaluate SELECT 1 WHERE NULL = NULL;
问题描述
我目前正在学习SQL.我有一个我想理解的书中的示例,但是MariaDB无法对其进行评估:
I'm currently in process of learning SQL. I have an example from a book that I'm trying to understand, but MariaDB cannot evaluate it:
SELECT 1
WHERE NULL = NULL
UNION
SELECT 0
WHERE NULL <> NULL;
这会产生以下错误:
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'WHERE NULL = NULL
UNION
SELECT 0
WHERE NULL <> NULL;' at line 2
我尝试过:
SELECT 1;
有效.但这不是:
SELECT 1 WHERE NULL = NULL;
我也尝试过添加括号,但这并没有太大帮助.我在这里做错了什么?此示例表明,将NULL与其他任何值进行比较都会得出未知".
I have also tried adding parantheses, but that didn't help much. What am I doing wrong here? This example was to show that comparing NULL with any other value gives "Unknown".
推荐答案
AFAIK,没有FROM
不能使用WHERE
. SELECT 1 WHERE 1 = 1
也将不起作用.
AFAIK you can not use WHERE
without FROM
. SELECT 1 WHERE 1 = 1
will also not work.
要修正您的示例,您可以从虚拟表中进行选择:
To fix your example you could select from a dummy table:
SELECT 1
FROM (SELECT 'dummy_value') dummy_table
WHERE NULL = NULL
UNION
SELECT 0
FROM (SELECT 'dummy_value') dummy_table
WHERE NULL <> NULL
但是了解MySQL行为的更好方法可能是
But a better way to see how MySQL behaves could be
SELECT
NULL = NULL,
NULL <> NULL,
NULL IS NULL,
NULL IS NOT NULL,
1 = NULL,
1 <> NULL,
1 IS NULL,
1 IS NOT NULL
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