常规

Questions

Questions and Answers

26.1.1:
When did MySQL 5.0 become production-ready
(GA)?

MySQL 5.0.15 was released for production use on 19 October
2005. We are now working on MySQL 5.1, which is currently in
beta.

在2005-10-19的时候我们已经释放出可以用于生产使用的MySQL 5.0.15了,现在我们正在开发MySQL 5.1 beta版本.

26.1.2:
Can MySQL 5.0 do subqueries?

Yes. See Section 13.2.8, “Subquery Syntax”.

当然了.请查看手册的子查询章节.

26.1.3:
Can MySQL 5.0 do multi-table inserts and
updates?

Yes. Multi-table UPDATE and
DELETE were actually implemented in MySQL
4.0, with enhancements added in MySQL 4.1. See
Section 13.2.10, “UPDATE Syntax”, and Section 13.2.1, “DELETE Syntax”.

是的.多表UPDATE和DELETE在MySQL 4.0的时候就已经实现了,并且在MySQL 4.1中得到了加强.详情请看 Section 13.2.10, “UPDATE Syntax” 和 Section 13.2.1, “DELETE Syntax”.

26.1.4:
Does MySQL 5.0 have a Query Cache? Does it work
on Server, Instance or Database?

Yes. The query cache operates on the server level, caching
complete result sets matched with the original query string.
If an exactly identical query is made (which often happens,
particularly in web applications), no parsing or execution
is necessary; the result is sent directly from the cache.
Various tuning options are available. See
Section 5.14, “The MySQL Query Cache”.

是的.查询缓存是基于服务器级别的,它缓存了匹配原始查询语句得到的全部结果集.如果提交了完全相同的查询语句(经常产生这种情况,尤其是在web应用中),无需解析语句和重新查询;结果直接从缓存中取得.可以通过各种参数来调整,详情请看 Section 5.14, “The MySQL Query Cache”.

26.1.5:
Does MySQL 5.0 have Sequences?

No. However, MySQL has an AUTO_INCREMENT
system, which in MySQL 5.0 can also handle
inserts in a multi-master replication setup. With the
--auto-increment-increment and
--auto-increment-offset startup options,
you can set each server to generate auto-increment values
that don't conflict with other servers. The
--auto-increment-increment value should be
greater than the number of servers, and each server should
have a unique offset.

不.不过MySQL支持AUTO_INCREMENT类型,在MySQL 5.0中还可以以此处理多主(multi-master)的复制.通过设置--auto-increment-increment 和 --auto-increment-offset 启动选项,就可以让多个主服务器产生不同的字增值,从而不会产生冲突.--auto-increment-increment 选项的值必须大于服务器的总数,并且每个服务器的值必须唯一.

26.1.6:
Does MySQL 5.0 have a NOW()
function with fractions of seconds?

不.这在MySQL的开发路线图中是"波动的特性".即这不是重要特性,不过在开发时间允许的情况会被实现.客户提出来的特定需求可能会导致我们改变开发计划.

尽管如此,MySQL不会把时间字符串解析成很细致.详情请看 Section 11.3.2, “The TIME Type”.

No. This is on the MySQL roadmap as a “rolling
feature”. This means that it is not a flagship
feature, but will be implemented, development time
permitting. Specific customer demand may change this
scheduling.

However, MySQL does parse time strings with a fractional
component. See Section 11.3.2, “The TIME Type”.

26.1.7:
Does MySQL 5.0 work with multi-core processors?

是的.MySQL完全支持多线程,当然也是支持多处理器(CPU)的了,不过首先得操作系统能支持才行.

Yes. MySQL is fully multi-threaded, and will make use of
multiple CPUs, provided that the operating system supports
them.

26.1.8:
Is there a hot backup tool for MyISAM like InnoDB Hot
Backup?

当前正在开发中.

This is currently under development for a future MySQL
release.

26.1.9:
Have there been there any improvements in error reporting
when foreign keys fail? Does MySQL now report which column
and reference failed?

MySQL每个主要发布版本中的Innodb的外键功能都会得到增强.MySQL 5.2中计划让所有的存储引擎都能支持外键;这就大大解决了当前存储引擎的不足之处了.

The foreign key support in InnoDB has
seen improvements in each major version of MySQL. Foreign
key support generic to all storage engines is scheduled for
MySQL 5.2; this should resolve any inadequacies in the
current storage engine specific implementation.

26.1.10:
Can MySQL 5.0 perform ACID transactions?

是的.当前所有的MySQL版本都支持事务.Innodb存储引擎完全支持行级锁的ACID事务,多版本,不锁表的可重复读,以及全部的标准SQL隔离级别.

NDB 存储引擎只支持 READ COMMITTED 事务隔离级别.

Yes. All current MySQL versions support transactions. The
InnoDB storage engine offers full ACID
transactions with row-level locking, multi-versioning,
non-locking repeatable reads, and all four SQL standard
isolation levels.

The NDB storage engine supports the
READ COMMITTED transaction isolation
level only.