Allow parsing of mysql empty row inserts

[Jefffrey]

Closes #624

Allows parsing of

INSERT INTO tb () VALUES ();

for MySql dialect

[coveralls]

Pull Request Test Coverage Report for Build 3816502109

• 61 of 61 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 86.06%

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Totals
Change from base Build 3801061789:	0.03%
Covered Lines:	13131
Relevant Lines:	15258

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💛 - Coveralls

[alamb]

Looks good to me - thanks @Jefffrey

I actually think we could allow the empty values list for all dialects (not just MySQL) per the https://github.com/sqlparser-rs/sqlparser-rs#syntax-vs-semantics section

That would keep this PR smaller and the sqlparser-rs code simpler

What do you think?

[alamb]

👍

[Jefffrey]

One thing I noticed however, was for postgresql it would be a parser exception. For example, when running:

insert into tb () values ();

Get exception

Caused by: org.postgresql.util.PSQLException: ERROR: syntax error at or near ")"
  Position: 17

Similarly, for the same in MSSql:

Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: Incorrect syntax near ')'.

So seems to suggest that for these dialects, it shouldn't parse at all. Thus, I'm a bit hesitant on enabling for all dialects. Not to mention, that the methods modified (parse_values() and parse_parenthesized_column_list()) are used in more places than just for parsing INSERT INTO statements (e.g. I believe parse_parenthesized_column_list() is used for parsing EXCEPT () for bigquery which requires it to be non-empty:

sqlparser-rs/tests/sqlparser_bigquery.rs

Lines 314 to 320 in 86d71f2

	assert_eq!(
	bigquery_and_generic()
	.parse_sql_statements("SELECT * EXCEPT () FROM employee_table")
	.unwrap_err()
	.to_string(),
	"sql parser error: Expected identifier, found: )"
	);

So those methods would still likely require the new allow_empty parameter so code might not be too simplified even if enabling the empty row insert for all dialects (unless refactor to a separate method specifically for INSERT INTO () tb VALUES () statements, if possible)

@alamb