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Naming and renaming MySQL files for case sensitivity

We have a Java-based product that uses JDBC to hit any relational databases, including MySQL. All was cool except when a client ran MySQL on Linux, and we ran into a file name case sensitive issue (not an issue on Windows). After digging we found that the Linux OS has case senstive file names. Since all of our SQL was uppercase, we simply changed the file names of the MySQL file names to uppercase, but this didn't fully fix the issue. What is the required or recommended method to name or rename MySQL files? Further, are there metadata files that actually hold pointers to the actual files that would need altering?

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When migrating an application or SQL script from using a Windows based MySQL server to a Linux or Unix based MySQL server, you may encounter error messages similar to the following:

mysql> SELECT * FROM city;

ERROR 1146 (42S02): Table 'world.city' doesn't exist
This error is encountered when your application has not used consistent case-sensitivity: a MySQL server running on Windows is not case-sensitive with regards to database and table names. For example, MySQL on Windows considers the city and City table references to refer to the same table. On Linux or Unix, the MySQL server will consider city and City to be two seperate tables.

Solution: If you have trouble remembering the allowable lettercase for database and table names, adopt a consistent convention, such as always creating databases and tables using lowercase names.

How table and database names are stored on disk and used in MySQL is defined by the lower_case_table_names system variable, which you can set when starting mysqld. lower_case_table_names can take one of the following values:

  • 0 - Table and database names are stored on disk using the lettercase specified in the CREATE TABLE or CREATE DATABASE statement. Name comparisons are case sensitive. This is the default on Unix systems. Note that if you force this to 0 with --lower-case-table-names=0 on a case-insensitive filesystem and access MyISAM tablenames using different lettercases, this may lead to index corruption.
  • 1 - Table names are stored in lowercase on disk and name comparisons are not case sensitive. MySQL converts all table names to lowercase on storage and lookup. This behavior also applies to database names as of MySQL 4.0.2, and to table aliases as of 4.1.1. This value is the default on Windows and Mac OS X systems.
  • 2 - Table and database names are stored on disk using the lettercase specified in the CREATE TABLE or CREATE DATABASE statement, but MySQL converts them to lowercase on lookup. Name comparisons are not case sensitive. Note: This works only on filesystems that are not case sensitive! InnoDB table names are stored in lowercase, as for lower_case_table_names=1. Setting lower_case_table_names to 2 can be done as of MySQL 4.0.18.
If you are using MySQL on only one platform, you don't normally have to change the lower_case_table_names variable. However, you may encounter difficulties if you want to transfer tables between platforms that differ in filesystem case sensitivity. For example, on Unix, you can have two different tables named my_table and MY_TABLE, but on Windows those names are considered the same. To avoid data transfer problems stemming from database or table name lettercase, you have two options:
  1. Use lower_case_table_names=1 on all systems. The main disadvantage with this is that when you use SHOW TABLES or SHOW DATABASES, you don't see the names in their original lettercase.
  2. Use lower_case_table_names=0 on Unix and lower_case_table_names=2 on Windows. This preserves the lettercase of database and table names. The disadvantage of this is that you must ensure that your queries always refer to your database and table names with the correct lettercase on Windows. If you transfer your queries to Unix, where lettercase is significant, they will not work if the lettercase is incorrect.
Note that before setting lower_case_table_names to 1 on Unix, you must first convert your old database and table names to lowercase before restarting mysqld.

This was first published in January 2005

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