feat: Support SHOW COLUMNS {FROM tbl} [FROM db] (#8)

* feat: Support SHOW COLUMNS FROM tbl FROM db

* Fix formatting in SHOW COLUMNS

Author: MazterQyou

src/parser.rs

@@ -3324,14 +3324,27 @@ impl<'a> Parser<'a> {
         self.expect_one_of_keywords(&[Keyword::COLUMNS, Keyword::FIELDS])?;
         self.expect_one_of_keywords(&[Keyword::FROM, Keyword::IN])?;
         let table_name = self.parse_object_name()?;
-        // MySQL also supports FROM <database> here. In other words, MySQL
-        // allows both FROM <table> FROM <database> and FROM <database>.<table>,
-        // while we only support the latter for now.
+        let double_from = self.parse_one_of_keywords(&[Keyword::FROM, Keyword::IN]);
+        let db_name = if double_from.is_some() {
+            Some(self.parse_object_name()?)
+        } else {
+            None
+        };
+        let object_name = match db_name {
+            Some(db_name) => ObjectName(
+                db_name
+                    .0
+                    .into_iter()
+                    .chain(table_name.0.into_iter())
+                    .collect(),
+            ),
+            None => table_name,
+        };
         let filter = self.parse_show_statement_filter()?;
         Ok(Statement::ShowColumns {
             extended,
             full,
-            table_name,
+            table_name: object_name,
             filter,
         })
     }

tests/sqlparser_mysql.rs

@@ -95,12 +95,10 @@ fn parse_show_columns() {
         .one_statement_parses_to("SHOW COLUMNS IN mytable", "SHOW COLUMNS FROM mytable");
     mysql_and_generic()
         .one_statement_parses_to("SHOW FIELDS IN mytable", "SHOW COLUMNS FROM mytable");
-
-    // unhandled things are truly unhandled
-    match mysql_and_generic().parse_sql_statements("SHOW COLUMNS FROM mytable FROM mydb") {
-        Err(_) => {}
-        Ok(val) => panic!("unexpected successful parse: {:?}", val),
-    }
+    mysql_and_generic().one_statement_parses_to(
+        "SHOW COLUMNS FROM mytable FROM mydb",
+        "SHOW COLUMNS FROM mydb.mytable",
+    );
 }
 
 #[test]