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MySQL Globalization  /  Character Sets, Collations, Unicode  /  Error Message Character Set

1.6 Error Message Character Set

This section describes how the MySQL server uses character sets for constructing error messages and returning them to clients. For information about the language of error messages (rather than the character set), see Section 1.11, “Setting the Error Message Language”. For general information about configuring error logging, see The Error Log.

The server constructs error messages using UTF-8 and returns them to clients in the character set specified by the character_set_results system variable. Clients can set character_set_results to control the character set in which they receive error messages. The variable can be set directly, or indirectly by means such as SET NAMES. For more information about character_set_results, see Section 1.4, “Connection Character Sets and Collations”.

The server constructs error messages as follows:

  • The message template uses UTF-8.

  • Parameters in the message template are replaced with values that apply to a specific error occurrence:

    • Identifiers such as table or column names use UTF-8 internally so they are copied as is.

    • Character (nonbinary) string values are converted from their character set to UTF-8.

    • Binary string values are copied as is for bytes in the range 0x20 to 0x7E, and using \x hexadecimal encoding for bytes outside that range. For example, if a duplicate-key error occurs for an attempt to insert 0x41CF9F into a VARBINARY unique column, the resulting error message uses UTF-8 with some bytes hexadecimal encoded:

      Duplicate entry 'A\xC3\x9F' for key 1

To return a message to the client after it has been constructed, the server converts it from UTF-8 to the character set specified by the character_set_results system variable. If character_set_results has a value of NULL or binary, no conversion occurs. No conversion occurs if the variable value is utf8, either, because that matches the original error message character set.

For characters that cannot be represented in character_set_results, some encoding may occur during the conversion. The encoding uses Unicode code point values:

  • Characters in the Basic Multilingual Plane (BMP) range (0x0000 to 0xFFFF) are written using \nnnn notation.

  • Characters outside the BMP range (0x10000 to 0x10FFFF) are written using \+nnnnnn notation.

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