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Updated on 2025-10-23 GMT+08:00
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Identifier Description

The M-compatible naming rules for identifiers are as follows:

  • Identifiers support backquotes (``) by default.
    • When sql_mode is set to ANSI_QUOTES, identifiers support backquotes (``) and double quotation marks ("").
    • In special cases, quotation marks can be used to avoid special character errors.
  • Characters allowed in unquoted identifiers are as follows:
    • ASCII: letters, digits (0-9), underscores (_), dollar signs ($), and number signs (#)
    • Extended characters: U+0080 to U+00FF
    • Only letters, digits, underscores (_), and extended characters from U+0080 to U+00FF are allowed at the beginning.
  • Characters allowed in quoted identifiers are as follows:
    • ASCII: U+0001 to U+007F
    • Extended characters: U+0080 to U+FFFF
  • Identifiers cannot be U+0000 characters or characters greater than U+10000.
  • An identifier can start with a digit but cannot consist of only digits unless it is enclosed in quotation marks.

The case sensitivity of M-compatible identifiers is as follows:

  • When the GUC parameter lower_case_table_names is set to 0, case-sensitive identifiers include databases, schemas, tables, and views. These identifiers must be case-sensitive during creation and use.
  • When the GUC parameter lower_case_table_names is set to 1, databases, schemas, tables (including the sequence names generated by the auto_increment column), and views are case-insensitive during creation and use. In addition, when backquotes or double quotation marks are used to qualify these objects, the objects are still case-insensitive.
  • Column names are case-sensitive when they are stored and are case-insensitive when they are used for comparison. Column names are stored as they are in the system and are case-insensitive when they are used.
  • Other identifiers:
    • They are lowercase in the system. If an identifier is enclosed in double quotation marks (SQL_MODE must be set to ANSI_QUOTES) or backquotes, it is case-sensitive.
    • If a schema or table is specified and the GUC parameter lower_case_table_names is set to 0, the schema and table names are case-sensitive. If the GUC parameter lower_case_table_names is set to 1, the schema and table names are case-insensitive.
Parent topic: SQL Syntax