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python MySQLdb模块安装 - 更多技术 - 清泛网 - 专注C/C++及内核技术
python MySQLdb模块安装python-MySQLdb-installMySQLdb是python操作mysql数据库的一个库．mysql的几乎所有的操作都可以实现，在python2系列使用Mysqldb,在python3系列使用pymysql和mysql connect。安装步骤如下：1 pip方式安 MySQLdb是python操作mysql数据库...
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 to avoid mysql 'Deadlock found when trying to get lock; try restarting transaction'
...AL 900 SECOND
ORDER BY id
) u;
Another thing to keep in mind is that mysql documentation suggest that in case of a deadlock the client should retry automatically. you can add this logic to your client code. (Say, 3 retries on this particular error before giving up).
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MySQL - UPDATE query based on SELECT Query
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You can actually do this one of two ways:
MySQL update join syntax:
UPDATE tableA a
INNER JOIN tableB b ON a.name_a = b.name_b
SET validation_check = if(start_dts > end_dts, 'VALID', '')
-- where clause can go here
ANSI SQL syntax:
UPDATE tableA SET validation...
MYSQL Truncated incorrect DOUBLE value
...ally whenever there is some Syntax issue it throws this useless exception "mysql-truncated-incorrect-double-value"
– heman123
May 10 '18 at 11:47
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Retrieving the last record in each group - MySQL
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MySQL 8.0 now supports windowing functions, like almost all popular SQL implementations. With this standard syntax, we can write greatest-n-per-group queries:
WITH ranked_messages AS (
SELECT m.*, ROW_NUMBER() OVER (PARTIT...
MySQL LIKE IN()?
...eing sufficient to give me the correct results, using LIKE as well allowed MySQL to reduce the result set considerably before having to use the slower REGEXP criteria.
– mpen
Feb 15 '12 at 0:11
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Tactics for using PHP in a high-load site
...l you measure and compare your changes.
For example, for many years, the MySQL query cache was the solution to all of our performance problems. If your site was slow, MySQL experts suggested turning the query cache on. It turns out that if you have a high write load, the cache is actually cripplin...
Does MySQL ignore null values on unique constraints?
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Yes, MySQL allows multiple NULLs in a column with a unique constraint.
CREATE TABLE table1 (x INT NULL UNIQUE);
INSERT table1 VALUES (1);
INSERT table1 VALUES (1); -- Duplicate entry '1' for key 'x'
INSERT table1 VALUES (NULL);...
#1071 - Specified key was too long; max key length is 1000 bytes
...The INT(1) and INT(32) data types indicates another misunderstanding about MySQL. The numeric argument has no effect related to storage or the range of values allowed for the column. INT is always 4 bytes, and it always allows values from -2147483648 to 2147483647. The numeric argument is about p...