Support specifying ASC/DESC in index columns (#249)

...by reusing `OrderByExpr` for `columns` in `Statement::CreateIndex`.

This supports SQLite's indexed-column syntax https://www.sqlite.org/syntax/indexed-column.html

MSSQL's (`ON <object> ( column [ ASC | DESC ] [ ,...n ] )`)
https://docs.microsoft.com/en-us/sql/t-sql/statements/create-index-transact-sql?view=sql-server-ver15

And most of PostgreSQL syntax (except for opclass):
`( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )`
https://www.postgresql.org/docs/12/sql-createindex.html

src/ast/mod.rs

@@ -498,7 +498,7 @@ pub enum Statement {
         /// index name
         name: ObjectName,
         table_name: ObjectName,
-        columns: Vec<Ident>,
+        columns: Vec<OrderByExpr>,
         unique: bool,
         if_not_exists: bool,
     },

src/parser.rs

@@ -1142,7 +1142,9 @@ impl Parser {
         let index_name = self.parse_object_name()?;
         self.expect_keyword(Keyword::ON)?;
         let table_name = self.parse_object_name()?;
-        let columns = self.parse_parenthesized_column_list(Mandatory)?;
+        self.expect_token(&Token::LParen)?;
+        let columns = self.parse_comma_separated(Parser::parse_order_by_expr)?;
+        self.expect_token(&Token::RParen)?;
         Ok(Statement::CreateIndex {
             name: index_name,
             table_name,

tests/sqlparser_common.rs

@@ -3152,8 +3152,19 @@ fn ensure_multiple_dialects_are_tested() {
 
 #[test]
 fn parse_create_index() {
-    let sql = "CREATE UNIQUE INDEX IF NOT EXISTS idx_name ON test(name,age)";
+    let sql = "CREATE UNIQUE INDEX IF NOT EXISTS idx_name ON test(name,age DESC)";
-    let ident_vec = vec![Ident::new("name"), Ident::new("age")];
+    let indexed_columns = vec![
+        OrderByExpr {
+            expr: Expr::Identifier(Ident::new("name")),
+            asc: None,
+            nulls_first: None,
+        },
+        OrderByExpr {
+            expr: Expr::Identifier(Ident::new("age")),
+            asc: Some(false),
+            nulls_first: None,
+        },
+    ];
     match verified_stmt(sql) {
         Statement::CreateIndex {
             name,
@@ -3164,7 +3175,7 @@ fn parse_create_index() {
         } => {
             assert_eq!("idx_name", name.to_string());
             assert_eq!("test", table_name.to_string());
-            assert_eq!(ident_vec, columns);
+            assert_eq!(indexed_columns, columns);
             assert_eq!(true, unique);
             assert_eq!(true, if_not_exists)
         }