From 71c3ec057b4701363ebecff0f2ac34b98e456f63 Mon Sep 17 00:00:00 2001
From: Alex Qyoun-ae <4062971+MazterQyou@users.noreply.github.com>
Date: Thu, 11 Aug 2022 14:42:08 +0400
Subject: [PATCH] Support `SHOW COLUMNS FROM tbl FROM db` (#562)

---
 src/parser.rs            | 14 ++++++++++----
 tests/sqlparser_mysql.rs | 10 ++++------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/src/parser.rs b/src/parser.rs
index a72529b1..e0324182 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -3739,10 +3739,16 @@ impl<'a> Parser<'a> {
         let full = self.parse_keyword(Keyword::FULL);
         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 object_name = self.parse_object_name()?;
+        let table_name = match self.parse_one_of_keywords(&[Keyword::FROM, Keyword::IN]) {
+            Some(_) => {
+                let db_name = vec![self.parse_identifier()?];
+                let ObjectName(table_name) = object_name;
+                let object_name = db_name.into_iter().chain(table_name.into_iter()).collect();
+                ObjectName(object_name)
+            }
+            None => object_name,
+        };
         let filter = self.parse_show_statement_filter()?;
         Ok(Statement::ShowColumns {
             extended,
diff --git a/tests/sqlparser_mysql.rs b/tests/sqlparser_mysql.rs
index 004b2c87..9ac775bd 100644
--- a/tests/sqlparser_mysql.rs
+++ b/tests/sqlparser_mysql.rs
@@ -110,12 +110,10 @@ 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]