在 MySQL 中，数据库对应于数据目录中的目录。数据库中的每个表至少对应于数据库目录中的一个文件（根据存储引擎的不同，可能还会有更多文件）。触发器也对应于文件。因此，底层操作系统的大小写敏感性会影响数据库、表和触发器名称的大小写敏感性。这意味着在 Windows 中这些名称不区分大小写，而在大多数 Unix 系统中则区分大小写。一个显著的例外是 macOS，它基于 Unix，但使用默认的文件系统类型（HFS），该类型不区分大小写。然而，macOS 也支持 UFS 卷，其与任何 Unix 系统一样区分大小写。参见 第 1.7.1 节，“MySQL 对标准 SQL 的扩展”。lower_case_table_names 系统变量也会影响服务器如何处理标识符的大小写敏感性，如本节后面所述。In MySQL, databases correspond to directories within the data directory. Each table within a database corresponds to at least one file within the database directory (and possibly more, depending on the storage engine). Triggers also correspond to files. Consequently, the case sensitivity of the underlying operating system plays a part in the case sensitivity of database, table, and trigger names. This means such names are not case-sensitive in Windows, but are case-sensitive in most varieties of Unix. One notable exception is macOS, which is Unix-based but uses a default file system type (HFS+) that is not case-sensitive. However, macOS also supports UFS volumes, which are case-sensitive just as on any Unix. See Section 1.7.1, “MySQL Extensions to Standard SQL”. The lower_case_table_names system variable also affects how the server handles identifier case sensitivity, as described later in this section.

mysql> SELECT * FROM my_table WHERE MY_TABLE.col=1;

分区、子分区、列、索引、存储过程、事件和资源组名称在任何平台上都不区分大小写，列别名也同样不区分大小写。Partition, subpartition, column, index, stored routine, event, and resource group names are not case-sensitive on any platform, nor are column aliases.

然而，日志文件组的名称是区分大小写的。这与标准 SQL 不同。However, names of logfile groups are case-sensitive. This differs from standard SQL.

默认情况下，表别名在 Unix 上区分大小写，但在 Windows 或 macOS 上则不区分大小写。下面的语句在 Unix 上无法工作，因为它同时将别名引用为 a 和 A：By default, table aliases are case-sensitive on Unix, but not so on Windows or macOS. The following statement would not work on Unix, because it refers to the alias both as a and as A:

mysql> SELECT col_name FROM tbl_name AS a
       WHERE a.col_name = 1 OR A.col_name = 2;

然而，同样的语句在 Windows 上是允许的。为了避免由于这些差异引起的问题，最好采用一致的约定，例如始终使用小写名称创建和引用数据库及表。为了最大限度的可移植性和易用性，推荐采用这种约定。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.

表和数据库名称在磁盘上的存储方式以及在 MySQL 中的使用方式受到 lower_case_table_names 系统变量的影响。lower_case_table_names 可以取下表所示的值。该变量 不会 影响触发器标识符的大小写敏感性。在 Unix 上，lower_case_table_names 的默认值为 0。在 Windows 上，默认值为 1。在 macOS 上，默认值为 2。How table and database names are stored on disk and used in MySQL is affected by the lower_case_table_names system variable. 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.

lower_case_table_names 只能在初始化服务器时配置。服务器初始化后，禁止更改 lower_case_table_names 设置。lower_case_table_names can only be configured when initializing the server. Changing the lower_case_table_names setting after the server is initialized is prohibited.

如果你只在一个平台上使用 MySQL，通常不需要使用除默认值之外的 lower_case_table_names 设置。然而，如果你想在文件系统大小写敏感性不同的平台之间传输表，可能会遇到困难。例如，在 Unix 上，你可以有两个不同的表分别命名为 my_table 和 MY_TABLE，但在 Windows 上，这两个名字被认为是相同的。为了避免因数据库或表名的字母大小写导致的数据传输问题，你有两个选择：If you are using MySQL on only one platform, you do not normally have to use a lower_case_table_names setting other than the default. 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:

如果对象名称的大写形式在二进制排序规则下相等，则可能会被认为是重复的。对于游标、条件、存储过程、函数、保存点、存储例程参数、存储程序局部变量和插件的名称，这一点是正确的。但对于列、约束、数据库、分区、使用 PREPARE 预处理的语句、表、触发器、用户以及用户定义变量的名称，则不适用。Object names may be considered duplicates if their uppercase forms are equal according to a binary collation. That is true for names of cursors, conditions, procedures, functions, savepoints, stored routine parameters, stored program local variables, and plugins. It is not true for names of columns, constraints, databases, partitions, statements prepared with PREPARE, tables, triggers, users, and user-defined variables.

文件系统的大小写敏感性可能会影响 INFORMATION_SCHEMA 表中字符串列的搜索。有关更多信息，请参阅 第 12.8.7 节，“在 INFORMATION_SCHEMA 搜索中使用排序规则”。File system case sensitivity can affect searches in string columns of INFORMATION_SCHEMA tables. For more information, see Section 12.8.7, “Using Collation in INFORMATION_SCHEMA Searches”.