F MySQL での既知のエラーと欠けているデザイン

• MIT-pthread を使用するとき、他のディレクトリでビルド出来ません。 これは MIT-pthread の変更を要求するため、我々は、これを修正しそうにないです。
• BLOB values can't ``reliably'' be used in GROUP BY or ORDER BY or DISTINCT. これらの場合、 BLOB の比較の際には最初の max_sort_length バイト （デフォルト1024）だけが使用されます。 これは mysqld の -O max_sort_length オプションで変更可能です。 A workaround for most cases is to use a substring: SELECT DISTINCT LEFT(blob,2048) FROM tbl_name.
• Calculation is done with BIGINT or DOUBLE (both are normally 64 bits long). It depends on the function which precision one gets. The general rule is that bit functions are done with BIGINT precision, IF, and ELT() with BIGINT or DOUBLE precision and the rest with DOUBLE precision. One should try to avoid using bigger unsigned long long values than 63 bits (9223372036854775807) for anything else than bit fields!
• 全ての文字型のフィールド、BLOB と TEXT はのぞいて、は、 検索されるときに最後についているスペースを自動で取り除きます。 CHAR 型ではこれは OK で、この特徴は ANSI SQL92 に従っていると見なされるでしょう。 MySQL のバグは、 VARCHAR でも同様に行ってしまうことです。
• 一つのテーブルに ENUM と SET フィールドは 255 までしか持てません。
• safe_mysqld re-directs all messages from mysqld to the mysqld log. One problem with this is that if you execute mysqladmin refresh to close and reopen the log, stdout and stderr are still redirected to the old log. If you use --log extensively, you should edit safe_mysqld to log to `'hostname'.err' instead of `'hostname'.log' so you can easily reclaim the space for the old log by deleting the old one and executing mysqladmin refresh.
• In the UPDATE statement, columns are updated from left to right. If you refer to a updated column, you will get the updated value instead of the original value. For example:

  mysql> UPDATE tbl_name SET KEY=KEY+1,KEY=KEY+1
  

  will update KEY with 2 instead of with 1.
• You can't use temporary tables more than once in the same query.

  select * from temporary_table, temporary_table as t2;
  

• Because MySQL allows you to work with table types that doesn't support transactions (and thus can't rollback data) some things behaves a little different in MySQL than in other SQL servers: (This is just to ensure that MySQL never need to do a rollback for a SQL command). This may be a little akward at times as column values must be checked in the application, but this will actually give you a nice speed increase as it allows MySQL to do some optimizations that otherwice would be hard to do. If you set a colum to a wrong value, MySQL will instead of doing a rollback instead store the best possible value in the column.
  • If you try to store a value outside of the range in a numerical column, MySQL will instead store the smallest or biggest possible value in the column.
  • If you try to store a string, that doesn't start with a number, into a numerical column MySQL will store 0 into it.
  • If you try to to store NULL into a column that doesn't take NULL values, MySQL will store 0 or '' (empty string) in it instead. (This behavour can however be changed with the -DDONT_USE_DEFAULT_FIELDS compile option).
  • MySQL allows you to store some wrong date values into DATE and DATETIME columns. (Like 2000-02-31 or 2000-02-00). If the date is totally wrong, MySQL will store the special 0000-00-00 date value in the column.
  • If you set an enum to an not supported value, it will be set to the error value 'empty string', with numeric value 0.

The following is known bugs in earlier versions of MySQL:

• You can get a hanged thread if you do a DROP TABLE on a table that is one among many tables that is locked with LOCK TABLES.
• In the following case you can get a core dump:
  1. Delayed insert handler has pending inserts to a table.
  2. LOCK table with WRITE
  3. FLUSH TABLES
• Before MySQL 3.23.2 an UPDATE that updated a key with a WHERE on the same key may have failed because the key was used to search for records and the same row may have been found multiple times:

  UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100;
  

  A workaround is to use:

  mysql> UPDATE tbl_name SET KEY=KEY+1 WHERE KEY+0 > 100;
  

  This will work because MySQL will not use index on expressions in the WHERE clause.
• MySQL 3.23 より前では、全ての数値型で、少数部分が削られてしまいます。 これは、そのフィールドが何桁の小数部を持つか、定義しなければならなかった、と いうことです。 全ての結果は10進の数で正しく返ってきました。

For platform-specific bugs, see the sections about compiling and porting.

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