Make COLUMN optional and fix whitespace handling in fmt::Display implementation

Author: nickolay

src/ast/ddl.rs

@@ -27,7 +27,7 @@ pub enum AlterTableOperation {
     AddColumn { column_def: ColumnDef },
     /// TODO: implement `DROP CONSTRAINT <name>`
     DropConstraint { name: Ident },
-    /// `DROP COLUMN [ IF EXISTS ] <column> [ CASCADE ]`
+    /// `DROP [ COLUMN ] [ IF EXISTS ] <column_name> [ CASCADE ]`
     DropColumn {
         column_name: Ident,
         if_exists: bool,
@@ -56,10 +56,10 @@ impl fmt::Display for AlterTableOperation {
                 cascade,
             } => write!(
                 f,
-                "DROP COLUMN {}{} {}",
-                if *if_exists { "IF EXISTS " } else { " " },
+                "DROP COLUMN {}{}{}",
+                if *if_exists { "IF EXISTS " } else { "" },
                 column_name,
-                if *cascade { "CASCADE" } else { "" }
+                if *cascade { " CASCADE" } else { "" }
             ),
             AlterTableOperation::RenameColumn {
                 old_column_name,

src/parser.rs

@@ -1341,17 +1341,14 @@ impl Parser {
                 }
             }
         } else if self.parse_keyword(Keyword::DROP) {
-            if self.parse_keyword(Keyword::COLUMN) {
-                let if_exists = self.parse_keywords(&[Keyword::IF, Keyword::EXISTS]);
-                let column_name = self.parse_identifier()?;
-                let cascade = self.parse_keyword(Keyword::CASCADE);
-                AlterTableOperation::DropColumn {
-                    column_name,
-                    if_exists,
-                    cascade,
-                }
-            } else {
-                return self.expected("a column in ALTER TABLE .. DROP", self.peek_token());
+            let _ = self.parse_keyword(Keyword::COLUMN);
+            let if_exists = self.parse_keywords(&[Keyword::IF, Keyword::EXISTS]);
+            let column_name = self.parse_identifier()?;
+            let cascade = self.parse_keyword(Keyword::CASCADE);
+            AlterTableOperation::DropColumn {
+                column_name,
+                if_exists,
+                cascade,
             }
         } else {
             return self.expected("ADD, RENAME, or DROP after ALTER TABLE", self.peek_token());

tests/sqlparser_common.rs

@@ -1391,6 +1391,14 @@ fn parse_alter_table_constraints() {
 #[test]
 fn parse_alter_table_drop_column() {
     check_one("DROP COLUMN IF EXISTS is_active CASCADE");
+    one_statement_parses_to(
+        "ALTER TABLE tab DROP IF EXISTS is_active CASCADE",
+        "ALTER TABLE tab DROP COLUMN IF EXISTS is_active CASCADE",
+    );
+    one_statement_parses_to(
+        "ALTER TABLE tab DROP is_active CASCADE",
+        "ALTER TABLE tab DROP COLUMN is_active CASCADE",
+    );
 
     fn check_one(constraint_text: &str) {
         match verified_stmt(&format!("ALTER TABLE tab {}", constraint_text)) {