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When should I use a composite index?
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@felwithe MySQL can only use one index per each of the tables in a query (Exemptions are there. eg, Merging of indexes). Which ideally means that a table in a query, must use a single index for all where-clause, table join, group-by an...
How do I check if a column is empty or null in MySQL?
...OR some_col = ' ' (one space inserted in the string) then it works on both MySQL and Oracle, see answer of "onedaywhen". some_col = '' doesn't work on Oracle as empty strings mean NULL there.
– Johanna
May 18 '15 at 14:07
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What can you use Python generator functions for?
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Real World Example
Let's say you have 100 million domains in your MySQL table, and you would like to update Alexa rank for each domain.
First thing you need is to select your domain names from the database.
Let's say your table name is domains and column name is domain.
If you use SELECT...
MySQL “between” clause not inclusive?
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From the MySQL-manual:
This is equivalent to the expression
(min <= expr AND expr <= max)
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How do I change the data type for a column in MySQL?
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http://dev.mysql.com/doc/refman/5.1/en/alter-table.html
ALTER TABLE tablename MODIFY columnname INTEGER;
This will change the datatype of given column
Depending on how many columns you wish to modify it might be best to generate a scri...
PDOException “could not find driver”
I have just installed Debian Lenny with Apache, MySQL, and PHP and I am receiving a PDOException could not find driver .
3...
从异构软件开发者的角度看异构计算 - 操作系统(内核) - 清泛网 - 专注C/C++...
...此我们应该先对异构的计算平台有一定理解，然后在了解如何在异构平台上执行计算。那到底什么是异构平台呢？首先我们知道现在有很多可以用于计算的单元，诸如CPU，GPU，MIC，DSP，FPGA等等，如果在同一个计算机系统中加入...
MySQL 启动报错 Table \'mysql.plugin\' doesn\'t exist - 数据库(内核) -...
MySQL 启动报错 Table 'mysql.plugin' doesn't exist 启动报错： opt szy bin mysqld: Table 'mysql.plugin ' doesn 't exist141211 15:06:12 [ERROR] Can 't open t...启动报错：
/opt/szy/bin/mysqld: Table \'mysql.plugin\' doesn\'t exist
141211 15:06:12 [ERROR] Can\'t open the mysql.plug...
MySQL Server has gone away when importing large sql file
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As stated here:
Two most common reasons (and fixes) for the MySQL server has gone away
(error 2006) are:
Server timed out and closed the connection. How to fix:
check that wait_timeout variable in your mysqld’s my.cnf configuration file is large enough. On Debian: su...
MySQL Error 1093 - Can't specify target table for update in FROM clause
...handle the OP's exact query, please see other answers to this question
In MySQL, you can't modify the same table which you use in the SELECT part.
This behaviour is documented at:
http://dev.mysql.com/doc/refman/5.6/en/update.html
Maybe you can just join the table to itself
If the logic is simple...