show variables like 'lower_case_table_names';


However, this same statement is permitted on Windows. To avoid problems caused by such differences, it is best to adopt a consistent convention, such as always creating and referring to databases and tables using lowercase names. This convention is recommended for maximum portability and ease of use.

How table and database names are stored on disk and used in MySQL is affected by the ​​​lower_case_table_names​​​​ system variable, which you can set when starting​​mysqld​​​. ​​​lower_case_table_names​​​ can take the values shown in the following table. This variable does not affect case sensitivity of trigger identifiers. On Unix, the default value of ​​​lower_case_table_names​​​ is 0. On Windows, the default value is 1. On macOS, the default value is 2.

Value

Meaning

​​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. You should not set this variable to 0 if you are running MySQL on a system that has case-insensitive file names (such as Windows or macOS). If you force this variable to 0 with ​​​--lower-case-table-names=0​​​​ on a case-insensitive file system and access ​​MyISAM​​ tablenames using different lettercases, index corruption may result.

​​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 and table aliases.

​​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. This works only on file systems that are not case-sensitive! ​​InnoDB​​​ table names and view names are stored in lowercase, as for ​​lower_case_table_names=1​​.

If you are using MySQL on only one platform, you do not normally have to change the ​​​lower_case_table_names​​​​ variable from its default value. However, you may encounter difficulties if you want to transfer tables between platforms that differ in file system case sensitivity. For example, on Unix, you can have two different tables named ​​my_table​​​ and ​​MY_TABLE​​, but on Windows these two names are considered identical. To avoid data transfer problems arising from lettercase of database or table names, you have two options:


  • 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 do not see the names in their original lettercase.
  • 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 statements always refer to your database and table names with the correct lettercase on Windows. If you transfer your statements to Unix, where lettercase is significant, they do not work if the lettercase is incorrect.
    Exception: If you are using ​​InnoDB​​ tables and you are trying to avoid these data transfer problems, you should set ​​​lower_case_table_names​​​ to 1 on all platforms to force names to be converted to lowercase.


变更​​​lower_case_table_names​​​ 操作

If you plan to set the ​​​lower_case_table_names​​​​ system variable to 1 on Unix, you must first convert your old database and table names to lowercase before stopping​​mysqld​​​ and restarting it with the new variable setting. To do this for an individual table, use ​​​RENAME TABLE​​​:

RENAME TABLE T1 TO t1;

To convert one or more entire databases, dump them before setting ​​​lower_case_table_names​​​​, then drop the databases, and reload them after setting​​​lower_case_table_names​​​:


  2. Use ​​mysqldump​​ to dump each database:
    ​​mysqldump --databases db1 > db1.sql mysqldump --databases db2 > db2.sql ...​​Do this for each database that must be recreated.
  3. Use ​​DROP DATABASE​​ to drop each database.
  4. Stop the server, set ​​​lower_case_table_names​​​, and restart the server.
  5. Reload the dump file for each database. Because ​​​lower_case_table_names​​​ is set, each database and table name is converted to lowercase as it is re-created:
    ​​mysql < db1.sql mysql < db2.sql ...​​