Add MSSQL dialect and fix up the postgres' identifier rules

The `@@version` test is MS' dialect of SQL, it seems, so test it with
its own dialect.

Update the rules for identifiers in Postresql dialect per documentation,
while we're at it. The current identifier rules in Postgresql dialect
were introduced in this commit - as a copy of generic rules, it seems:
810cd8e6cf (diff-2808df0fba0aed85f9d35c167bd6a5f1L138)

src/dialect/generic_sql.rs

@@ -5,7 +5,7 @@ pub struct GenericSqlDialect {}
 
 impl Dialect for GenericSqlDialect {
     fn is_identifier_start(&self, ch: char) -> bool {
-        (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '@'
+        (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_' || ch == '#' || ch == '@'
     }
 
     fn is_identifier_part(&self, ch: char) -> bool {
@@ -13,6 +13,8 @@ impl Dialect for GenericSqlDialect {
             || (ch >= 'A' && ch <= 'Z')
             || (ch >= '0' && ch <= '9')
             || ch == '@'
+            || ch == '$'
+            || ch == '#'
             || ch == '_'
     }
 }

src/dialect/mod.rs

@@ -1,12 +1,14 @@
 mod ansi_sql;
 mod generic_sql;
 pub mod keywords;
+mod mssql;
 mod postgresql;
 
 use std::fmt::Debug;
 
 pub use self::ansi_sql::AnsiSqlDialect;
 pub use self::generic_sql::GenericSqlDialect;
+pub use self::mssql::MsSqlDialect;
 pub use self::postgresql::PostgreSqlDialect;
 
 pub trait Dialect: Debug {

src/dialect/mssql.rs

@@ -0,0 +1,22 @@
+use crate::dialect::Dialect;
+
+#[derive(Debug)]
+pub struct MsSqlDialect {}
+
+impl Dialect for MsSqlDialect {
+    fn is_identifier_start(&self, ch: char) -> bool {
+        // See https://docs.microsoft.com/en-us/sql/relational-databases/databases/database-identifiers?view=sql-server-2017#rules-for-regular-identifiers
+        // We don't support non-latin "letters" currently.
+        (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_' || ch == '#' || ch == '@'
+    }
+
+    fn is_identifier_part(&self, ch: char) -> bool {
+        (ch >= 'a' && ch <= 'z')
+            || (ch >= 'A' && ch <= 'Z')
+            || (ch >= '0' && ch <= '9')
+            || ch == '@'
+            || ch == '$'
+            || ch == '#'
+            || ch == '_'
+    }
+}

src/dialect/postgresql.rs

@@ -5,14 +5,17 @@ pub struct PostgreSqlDialect {}
 
 impl Dialect for PostgreSqlDialect {
     fn is_identifier_start(&self, ch: char) -> bool {
-        (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '@'
+        // See https://www.postgresql.org/docs/11/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
+        // We don't yet support identifiers beginning with "letters with
+        // diacritical marks and non-Latin letters"
+        (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_'
     }
 
     fn is_identifier_part(&self, ch: char) -> bool {
         (ch >= 'a' && ch <= 'z')
             || (ch >= 'A' && ch <= 'Z')
             || (ch >= '0' && ch <= '9')
-            || ch == '@'
+            || ch == '$'
             || ch == '_'
     }
 }

src/test_utils.rs

@@ -103,6 +103,7 @@ pub fn all_dialects() -> TestedDialects {
         dialects: vec![
             Box::new(GenericSqlDialect {}),
             Box::new(PostgreSqlDialect {}),
+            Box::new(MsSqlDialect {}),
             Box::new(AnsiSqlDialect {}),
         ],
     }