Backporting Placeholder support for Cube Store (#420)

[ovr]

No description provided.

[ovr]

cargo fmt))

[coveralls]

Pull Request Test Coverage Report for Build 4700225395

• 26 of 31 (83.87%) changed or added relevant lines in 4 files are covered.
• 49 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-6.8%) to 82.368%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser.rs	3	4	75.0%
tests/sqlparser_common.rs	16	17	94.12%
src/tokenizer.rs	6	9	66.67%

Files with Coverage Reduction	New Missed Lines	%
src/parser.rs	1	84.51%
src/ast/mod.rs	2	70.48%
src/ast/query.rs	2	85.07%
tests/sqlparser_snowflake.rs	2	96.43%
tests/sqlparser_postgres.rs	8	97.06%
tests/sqlparser_common.rs	34	97.2%

Totals
Change from base Build 1513769481:	-6.8%
Covered Lines:	5615
Relevant Lines:	6817

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💛 - Coveralls