Support DROP CONSTRAINT [ IF EXISTS ] <name> [ CASCADE ] (#396)

* adding support for DROP CONSTRAINT [ IF EXISTS ] <name>

* implementing [ CASCADE ] for DROP CONSTRAINT

src/ast/ddl.rs

@@ -32,8 +32,12 @@ pub enum AlterTableOperation {
     AddConstraint(TableConstraint),
     /// `ADD [ COLUMN ] <column_def>`
     AddColumn { column_def: ColumnDef },
-    /// TODO: implement `DROP CONSTRAINT <name>`
+    /// `DROP CONSTRAINT [ IF EXISTS ] <name>`
-    DropConstraint { name: Ident },
+    DropConstraint {
+        if_exists: bool,
+        name: Ident,
+        cascade: bool,
+    },
     /// `DROP [ COLUMN ] [ IF EXISTS ] <column_name> [ CASCADE ]`
     DropColumn {
         column_name: Ident,
@@ -107,7 +111,19 @@ impl fmt::Display for AlterTableOperation {
                 display_comma_separated(partitions),
                 ie = if *if_exists { " IF EXISTS" } else { "" }
             ),
-            AlterTableOperation::DropConstraint { name } => write!(f, "DROP CONSTRAINT {}", name),
+            AlterTableOperation::DropConstraint {
+                if_exists,
+                name,
+                cascade,
+            } => {
+                write!(
+                    f,
+                    "DROP CONSTRAINT {}{}{}",
+                    if *if_exists { "IF EXISTS " } else { "" },
+                    name,
+                    if *cascade { " CASCADE" } else { "" },
+                )
+            }
             AlterTableOperation::DropColumn {
                 column_name,
                 if_exists,

src/parser.rs

@@ -2030,6 +2030,15 @@ impl<'a> Parser<'a> {
                     partitions,
                     if_exists: false,
                 }
+            } else if self.parse_keyword(Keyword::CONSTRAINT) {
+                let if_exists = self.parse_keywords(&[Keyword::IF, Keyword::EXISTS]);
+                let name = self.parse_identifier()?;
+                let cascade = self.parse_keyword(Keyword::CASCADE);
+                AlterTableOperation::DropConstraint {
+                    if_exists,
+                    name,
+                    cascade,
+                }
             } else {
                 let _ = self.parse_keyword(Keyword::COLUMN);
                 let if_exists = self.parse_keywords(&[Keyword::IF, Keyword::EXISTS]);

tests/sqlparser_common.rs

@@ -2077,6 +2077,54 @@ fn parse_alter_table_alter_column_type() {
     );
 }
 
+#[test]
+fn parse_alter_table_drop_constraint() {
+    let alter_stmt = "ALTER TABLE tab";
+    match verified_stmt("ALTER TABLE tab DROP CONSTRAINT constraint_name CASCADE") {
+        Statement::AlterTable {
+            name,
+            operation:
+                AlterTableOperation::DropConstraint {
+                    name: constr_name,
+                    if_exists,
+                    cascade,
+                },
+        } => {
+            assert_eq!("tab", name.to_string());
+            assert_eq!("constraint_name", constr_name.to_string());
+            assert!(!if_exists);
+            assert!(cascade);
+        }
+        _ => unreachable!(),
+    }
+    match verified_stmt("ALTER TABLE tab DROP CONSTRAINT IF EXISTS constraint_name") {
+        Statement::AlterTable {
+            name,
+            operation:
+                AlterTableOperation::DropConstraint {
+                    name: constr_name,
+                    if_exists,
+                    cascade,
+                },
+        } => {
+            assert_eq!("tab", name.to_string());
+            assert_eq!("constraint_name", constr_name.to_string());
+            assert!(if_exists);
+            assert!(!cascade);
+        }
+        _ => unreachable!(),
+    }
+
+    let res = Parser::parse_sql(
+        &GenericDialect {},
+        &format!("{} DROP CONSTRAINT is_active TEXT", alter_stmt),
+    );
+    assert_eq!(
+        ParserError::ParserError("Expected end of statement, found: TEXT".to_string()),
+        res.unwrap_err()
+    );
+}
+
 #[test]
 fn parse_bad_constraint() {
     let res = parse_sql_statements("ALTER TABLE tab ADD");