* Overhaul the MySQL lexer
Fixes #975, #1063, #1453
Changes include:
Documentation
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* Note in the lexer docstring that Oracle MySQL is the target syntax.
MariaDB syntax is not a target (though there is significant overlap).
Unit tests
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* Add 140 unit tests for MySQL.
Literals
--------
* Hexadecimal/binary/date/time/timestamp literals are supported.
* Integer mantissas are supported for scientific notation.
* In-string escapes are now tokenized properly.
* Support the "unknown" constant.
Comments
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* Optimizer hints are now supported, and keywords are
recognized and tokenized as preprocessor instructions.
* Remove nested multi-line comment support, which is no
longer supported in MySQL.
Variables
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* Support the '@' prefix for variable names.
* Lift restrictions on characters in unquoted variable names.
(MySQL does not impose a restriction on lead characters.)
* Support single/double/backtick-quoted variable names, including escapes.
* Support the '@@' prefix for system variable names.
* Support '?' as a variable so people can demonstrate prepared statements.
Keywords
--------
* Keyword / data type / function are now in a separate, auto-updating file.
* Support 25 additional data types (including spatial and JSON types).
* Support 460 additional MySQL keywords.
* Support 372 MySQL functions.
Explicit function support resolves a bug that causes non-function
items to be treated as functions simply because they have a trailing
opening parenthesis.
* Support exceptions for the 'SET' keyword, which is both a datatype and
a keyword depending on context.
Schema object names
-------------------
* Support Unicode in MySQL schema object names.
* Support parsing of backtick-quoted schema object name escapes.
(Escapes do not produce a distinct token type at this time.)
Operators
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* Remove non-operator characters from the list of operators.
* Remove non-punctuation characters from the list of punctuation.
* Cleanup items based on feedback
* Remove an unnecessary optional newline lookahead for single-line comments