Questions

Questions and Answers

26.1.1: When did MySQL 5.1 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.

26.1.2: Can MySQL 5.1 do subqueries?

Yes. See 項12.2.8. 「サブクエリ構文」.

26.1.3: Can MySQL 5.1 peform multi-table inserts, updates, and deletes?

Yes. For the syntax required to perform multi-table updates, see 項12.2.10. 「UPDATE 構文」; for that required to perform multi-table deletes, see 項12.2.1. 「DELETE 構文」.

A multi-table insert can be accomplished using a trigger whose FOR EACH ROW clause contains multiple INSERT statements within a BEGIN ... END block. See 項18.3. 「トリガの使用」.

26.1.4: Does MySQL 5.1 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 項4.13. 「MySQL クエリ キャッシュ」.

26.1.5: Does MySQL 5.1 have Sequences?

No. However, MySQL has an AUTO_INCREMENT system, which in MySQL 5.1 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.

26.1.6: Does MySQL 5.1 have a NOW() function with fractions of seconds?

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 項10.3.2. 「TIME タイプ」.

26.1.7: Does MySQL 5.1 work with multi-core processors?

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?

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?

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 5.1 perform ACID transactions?

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.