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MySQL Orderby a number, Nulls last
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MySQL has an undocumented syntax to sort nulls last. Place a minus sign (-) before the column name and switch the ASC to DESC:
SELECT * FROM tablename WHERE visible=1 ORDER BY -position DESC, id DESC
It is essentially the...
Alter MySQL table to add comments on columns
I have been checking the MySQL Documentation for ALTER TABLE and it does not seem to include a way to add or modify a comment to a column. How can I do this?
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理解和配置 Linux 下的 OOM Killer - 操作系统(内核) - 清泛网 - 专注C/C++及内核技术
...M Killerhow-to-configure-the-linux-oom-killer最近有位 VPS 客户抱怨 MySQL 无缘无故挂掉，还有位客户抱怨 VPS 经常死机，登陆到终端看了一下，都是常见的 Out of memory 问题。这通常是因为某时刻应用程序大量请求 最近有位 VPS 客户抱怨 MySQ...
How to update column with null value
I am using mysql and need to update a column with a null value. I have tried this many different ways and the best I have gotten is an empty string.
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ROW_NUMBER() in MySQL
Is there a nice way in MySQL to replicate the SQL Server function ROW_NUMBER() ?
24 Answers
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Set NOW() as Default Value for datetime datatype?
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As of MySQL 5.6.5, you can use the DATETIME type with a dynamic default value:
CREATE TABLE foo (
creation_time DATETIME DEFAULT CURRENT_TIMESTAMP,
modification_time DATETIME ON UPDATE CURRENT_TIMESTAMP
)
Or even...
MySQL - Make an existing Field Unique
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ALTER IGNORE TABLE mytbl ADD UNIQUE (columnName);
For MySQL 5.7.4 or later:
ALTER TABLE mytbl ADD UNIQUE (columnName);
As of MySQL 5.7.4, the IGNORE clause for ALTER TABLE is removed and
its use produces an error.
So, make sure to remove duplicate entries first as IGNO...
Why does MYSQL higher LIMIT offset slow the query down?
...30
) q
JOIN mytable t
ON t.id = q.id
See this article:
MySQL ORDER BY / LIMIT performance: late row lookups
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MySQL selecting yesterday's date
... would otherwise require a cumbersome and wordy case statement, is that in mysql boolean values are 1 for true and 0 for false, so summing a condition effectively counts how many times it's true. Using this pattern can neaten up your SQL code.
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MySQL: selecting rows where a column is null
...E userid = NULL;
This will not give you the expected result, because from mysql doc
In SQL, the NULL value is never true in comparison to any other value, even NULL. An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for the operators and ...