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MySQL WHERE: how to write “!=” or “not equals”?
...ered Jul 10 '12 at 20:53
RolandoMySQLDBARolandoMySQLDBA
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STL 算法 - C/C++ - 清泛网 - 专注C/C++及内核技术
...合算法(4个)
函数名
头文件
函数功能
set_union
<algorithm>
构造一个有序序列，包含两个序列中所有的不重复元素。重载版本使用自定义的比较操作
函数原形
template<class InIt1, class InIt2, class OutIt> OutIt set_union...
UPDATE multiple tables in MySQL using LEFT JOIN
...plete orders: performance of LEFT JOIN compared to NOT IN
Unfortunately, MySQL does not allow using the target table in a subquery in an UPDATE statement, that's why you'll need to stick to less efficient LEFT JOIN syntax.
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MySQL: Order by field size/length
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@mastazi according to MySQL documentation: OCTET_LENGTH() is a synonym for LENGTH().
– Heitor
Oct 1 '17 at 5:35
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mysql Foreign key constraint is incorrectly formed error
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mysql error texts doesn't help so much, in my case, the column had "not null" constraint, so the "on delete set null" was not allowed
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MySql - Way to update portion of a string?
I'm looking for a way to update just a portion of a string via MySQL query.
4 Answers
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How can I use mySQL replace() to replace strings in multiple records?
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Are there any easy and safe tools to create mysql stored procedure?
– Ivan Slaughter
May 1 '17 at 18:28
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Insert into a MySQL table or update if exists
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Check out REPLACE
http://dev.mysql.com/doc/refman/5.0/en/replace.html
REPLACE into table (id, name, age) values(1, "A", 19)
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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
...cally, a lot of dbms have been quite poor when it comes to handling joins (MySQL being a particularly noteworthy example). So n+1 has, often, been notably faster than a join. And then there are ways to improve on n+1 but still without needing a join, which is what the original problem relates to.
H...
Ordering by the order of values in a SQL IN() clause
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Use MySQL's FIELD() function:
SELECT name, description, ...
FROM ...
WHERE id IN([ids, any order])
ORDER BY FIELD(id, [ids in order])
FIELD() will return the index of the first parameter that is equal to the first parameter (o...