feat: Introduce support for EXPLAIN/ANALYZE

[ovr]

Hello!

Thanks

[coveralls]

Pull Request Test Coverage Report for Build 443038537

• 86 of 91 (94.51%) changed or added relevant lines in 4 files are covered.
• 32 unchanged lines in 10 files lost coverage.
• Overall coverage decreased (-0.6%) to 91.363%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/mod.rs	10	11	90.91%
tests/sqlparser_common.rs	22	23	95.65%
src/parser.rs	6	9	66.67%

Files with Coverage Reduction	New Missed Lines	%
src/dialect/ansi.rs	1	85.71%
src/test_utils.rs	1	82.81%
src/dialect/mysql.rs	2	80.0%
src/dialect/postgresql.rs	2	75.0%
src/dialect/snowflake.rs	2	75.0%
src/dialect/sqlite.rs	2	80.0%
src/dialect/generic.rs	4	60.0%
src/dialect/mssql.rs	4	66.67%
src/parser.rs	4	88.82%
src/ast/mod.rs	10	77.78%

Totals
Change from base Build 303848626:	-0.6%
Covered Lines:	4845
Relevant Lines:	5303

---

💛 - Coveralls

[ovr]

Hello @Dandandan @nickolay

Can you please take a look?

Thanks!

[Dandandan]

Thanks for your PR @ovr ! Looking good. I left some review comments

[ovr]

@Dandandan, Thank for your comments, I've updated PR. Added ExplainLevel enum to support VERBOSE/ANALYZE levels.

[Dandandan]

I think it's not an enum but rather a combination of options.
see: https://www.postgresql.org/docs/9.1/sql-explain.html

I think all the following are correct:

EXPLAIN
EXPLAIN ANALYZE
EXPLAIN VERBOSE
EXPLAIN ANALYZE VERBOSE

So maybe this would be a better encoding?

Explain {
    analyze: bool
    verbose: bool
}

[ovr]

Yeap, you are right.

I checked What combintations work with PostgreSQL:

EXPLAIN VERBOSE SELECT * from test;
EXPLAIN ANALYSE SELECT * from test;
EXPLAIN ANALYZE VERBOSE SELECT * from test;

What doesnt work:

EXPLAIN VERBOSE ANALYZE SELECT * from test;

Find very funny thing, that they support ANALYSE, but it's not mentioned inside docs.

I've updated my PR.

[Dandandan]

Thanks a lot @ovr for your contribution!