SpirirHost Support Centre: MySQL Reference Manual p.41

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 1: General Information 41 BDB tables are a bit slow to open. If you have many BDB tables in a database, it will take a long time to use the mysql client on the database if you are not using the -A option or if you are using rehash. This is especially notable when you have a big table cache. The current replication protocol cannot deal with LOAD DATA INFILE and line termina- tor characters of more than 1 character. The following problems are known and will be xed in due time: When using SET CHARACTER SET, one can't use translated characters in database, table, and column names. If you have a DECIMAL column with a number stored in dierent formats (+01.00, 1.00, 01.00), GROUP BY may regard each value as a dierent value. DELETE FROM merge_table used without a WHERE will only clear the mapping for the table, not delete everything in the mapped tables. You cannot build the server in another directory when using MIT-pthreads. Because this requires changes to MIT-pthreads, we are not likely to x this. See Section 2.3.6 [MIT-pthreads], page 89. BLOB values can't \reliably" be used in GROUP BY or ORDER BY or DISTINCT. Only the rst max_sort_length bytes (default 1024) are used when comparing BLOBs in these cases. This can be changed with the -O max_sort_length option to mysqld. 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 unsigned long long values if they resolve to be bigger than 63 bits (9223372036854775807) for anything else than bit elds! MySQL Server 4.0 has better BIGINT handling than 3.23. All string columns, except BLOB and TEXT columns, automatically have all trailing spaces removed when retrieved. For CHAR types this is okay, and may be regarded as a feature according to ANSI SQL92. The bug is that in MySQL Server, VARCHAR columns are treated the same way. You can only have up to 255 ENUM and SET columns in one table. safe_mysqld redirects 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 an 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; This will update KEY with 2 instead of with 1.

MySQL Reference Manual

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