Add benchmarks using cargo bench / criterion (#190)

Author: Dandandan

docs/benchmarking.md

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+# Benchmarking
+
+Run `cargo bench` in the project `sqlparser_bench` execute the queries.
+It will report results using the `criterion` library to perform the benchmarking.
+
+The bench project lives in another crate, to avoid the negative impact on building the `sqlparser` crate.

sqlparser_bench/Cargo.toml

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+[package]
+name = "sqlparser_bench"
+version = "0.1.0"
+authors = ["Dandandan <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+sqlparser = { path = "../", version = "0.5.1-alpha-0" }
+
+[dev-dependencies]
+criterion = {version = "0.3"}
+
+[[bench]]
+name = "sqlparser_bench"
+harness = false

sqlparser_bench/benches/sqlparser_bench.rs

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+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use criterion::{criterion_group, criterion_main, Criterion};
+use sqlparser::dialect::GenericDialect;
+use sqlparser::parser::Parser;
+
+fn basic_queries(c: &mut Criterion) {
+    let mut group = c.benchmark_group("sqlparser-rs parsing benchmark");
+    let dialect = GenericDialect {};
+
+    let string = "SELECT * FROM table WHERE 1 = 1";
+    group.bench_function("sqlparser::select", |b| {
+        b.iter(|| Parser::parse_sql(&dialect, string));
+    });
+
+    let with_query = "
+        WITH derived AS (
+            SELECT MAX(a) AS max_a,
+                   COUNT(b) AS b_num,
+                   user_id
+            FROM TABLE
+            GROUP BY user_id
+        )
+        SELECT * FROM table
+        LEFT JOIN derived USING (user_id)
+    ";
+    group.bench_function("sqlparser::with_select", |b| {
+        b.iter(|| Parser::parse_sql(&dialect, with_query));
+    });
+}
+
+criterion_group!(benches, basic_queries);
+criterion_main!(benches);

sqlparser_bench/src/lib.rs

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+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}